May 11, 2006 - England is required to formally audit the screening histories of women diagnosed with invasive cervical cancer in their region.1 There are also ...
137
ORIGINAL ARTICLE
A new method for the classification of invasive cervical cancer screening histories Helen Bagnall, Philippa Pearmain, Joanne Clare and Gill Lawrence .................................................................................................. J Med Screen 2006;13:137–147
See end of article for authors’ affiliations
............... Correspondence to: Dr Gill Lawrence, Cervical Screening QA Reference Centre, West Midlands Cancer Intelligence Unit, Public Health Building, The University of Birmingham, Birmingham B15 2TT, UK; gill.lawrence @wmciu.nhs.uk Accepted for publication 11 May 2006
...............
Objectives To examine the ability of existing classification systems to provide screening histories for invasive cervical cancers which can be used in the evaluation of the NHS Cervical Screening Programme (NHSCSP), and to provide the diagnostic route data item required for the National Cancer Data Set (NCDS). Methods The ability of existing classification systems to derive unique, consistent screening histories for a cohort of invasive cervical cancers diagnosed in the West Midlands region in the period 2000–03 was tested using two separate timelines for women on normal routine recall (usually 3 or 5 years) and those on early recall having had an inadequate, low-grade abnormal or negative smear. Results Neither of the existing classification systems was capable of adequately categorizing all invasive cervical cancers. An original classification system incorporating features from the existing systems was therefore developed. This system includes both a ‘screening status’ component that essentially describes the status of a woman’s interaction with the NHSCSP at the time her cancer was diagnosed, and a ‘screening history’ component that describes the results of previous screening tests. Conclusions National adoption of this new screening histories classification system would provide a detailed, consistent, nationally comparable screening history for all invasive cervical cancers which can be used in the national and regional evaluation of the NHSCSP and in local audit by clinical teams supplemented by histology and colposcopy data. The classification categories could be collapsed down to provide the diagnostic route data item required for the NCDS.
INTRODUCTION
I
n addition to ongoing local audit undertaken in laboratories and colposcopy clinics, each Cervical Screening Quality Assurance Reference Centre (QARC) in England is required to formally audit the screening histories of women diagnosed with invasive cervical cancer in their region.1 There are also plans to implement a national audit of invasive cervical cancers by combining the screening histories data obtained and analysed by each regional QARC. The results of such audits could be used to assist in the identification of aspects of screening (attendance, screening interval, cervical sample reading, follow-up of abnormal results), which could be improved in order to further reduce the incidence of invasive cervical cancer. The audit results could also be used to derive the diagnostic route data item required in the National Cancer Data Set (NCDS)2 for each invasive cervical cancer. The usefulness of the data derived from invasive cervical cancer audits will, however, depend largely on the ease and consistency with which the classification system used can be interpreted and applied to all invasive cervical cancers, and on the quality and completeness of the information provided as part of the audit process. Historically, two classification systems for invasive cervical cancers have been described. The first system was included in the 1995 NHSCSP Achievable Standards for Cervical Cytopathology (ABC One).3 The ABC One system classifies the woman’s screening history by describing whether she has attended for screening in the last six months to five years and, if so, whether the cytology was negative,
www.jmedscreen.com
abnormal or inadequate. It also includes a category for previous treatment for cervical intraepithelial neoplasia (CIN). The second system was used in the pilot phase of a National Co-ordinating Network (NCN) project, the results of which were reported by Sasieni et al.4 in 1996. The NCN system, which was designed to compare the screening histories of women who have and have not been diagnosed with invasive cervical cancer, broadly classifies women as having no screening history, a negative screening history, a screening history including one borderline or mildly abnormal (low grade) result or a cytology result warranting referral for colposcopy. Both of the existing systems were developed at a time when the validity and consistency of the information held on the call and recall system precluded its use in a routine screening histories classification system. This paper describes a screening history classification system that has been developed by the West Midlands QARC (WMQARC) and examines its ability, relative to the ABC One and NCN classifications, to derive unique, consistent screening histories for women in the West Midlands diagnosed with invasive cervical cancer. In the WM system, each invasive cervical cancer is firstly allocated a ‘screening status’ which essentially describes the status of the woman’s interaction with the NHSCSP at the time her cancer was diagnosed (‘not eligible’, ‘diagnosed before invited’, ‘non-attender’, ‘lapsed’, ‘defaulter’, ‘screen detected’, ‘delayed screen detected’ and ‘interval’). Both the ‘screen detected’ and ‘screen detected delayed’ categories identify that the cancer was detected as a direct result of a screening test taken at the correct interval for the individual women. These eight ‘screening status’ categories can be
Journal of Medical Screening
2006
Volume 13
Number 3
138
Bagnall et al.
collapsed down to provide the four categories required for the NCDS (cancers detected by a national screening programme, interval cancers occurring in patients screened by a national screening programme, other cancers, and unknown). The WM system also provides a ‘screening history’ category for each cancer based on the woman’s smear history. This allows for the further subclassification of women on the basis of their previous screening results; facilitating, for example, more detailed investigation of women with ‘screen detected’ or ‘interval’ cancers, and the identification of women whose invasive cancers were diagnosed after a series of negative results or after the previous diagnosis and treatment of non-invasive disease. These subgroups can then form the basis of more detailed local audit and the ascertainment of previous histology and colposcopy data which are essential for a full case review.
METHODS Derivation of ‘screening status’category In line with the draft national service level agreement concerning the transfer of confidential data between cancer registries and screening QARCs, which is a Patient Information Advisory Group (PIAG) approved activity for the national cancer screening programmes, all cases of invasive cervical cancer recorded on the cancer registration database held by the West Midlands Cancer Intelligence Unit (WMCIU) with diagnosis dates during the period 1988–2003 were transferred to the WMQARC. The downloaded data contained the full demographic details required to match each case on the cervical screening call and recall computer systems using the ‘Open Exeter’ secure look-up facility.5 This provides the WMQARC with the means to search all call and recall systems within the WM in order to obtain the smear results held for a woman, regardless of whether she has moved residence within the region. To derive a full screening history, the following information was required for each case: the date of birth, the date of diagnosis of the invasive cancer, the date that all smears were taken together with the sender code of the organization where the smear was taken (in order to identify hospital smears), each cytology result and each recommended repeat interval. From this information, the most recent screen occurring before the invasive cervical cancer was diagnosed was identified, and a ‘screening status’ at diagnosis based on a classification system used by the West Midlands Breast Screening QARC6 was assigned to each cancer using the two timelines shown in Figure 1 as appropriate. The first timeline is for women who are on normal routine recall (usually three or five years) and the second is for women who are on early recall having had an inadequate, lowgrade abnormal or negative smear. Table 1 summarizes the ‘screening status’ at diagnosis categories developed for invasive cervical cancers by applying the breast screening status classification system. The invasive cervical cancer ‘screening status’ classification system depends on identifying the most recent screening result before the invasive disease was diagnosed and, if it recommended referral, identifying whether it was probably taken in response to symptoms or whether it was more likely to have been taken in response to an invitation from the NHSCSP. Once this assessment has been made, smears recommending referral that are identified as being symptomatic are excluded. Where the last smear taken before diagnosis recommends referral, the time interval between the last two recorded smears is calculated. If the woman has Journal of Medical Screening
2006
Volume 13
Number 3
attended for the referring smear at the recommended time interval (e.g. three years if she was on three-year routine recall), this smear is assumed to be routine and is included. In this case the cancer was detected as a result of attending the NHSCSP and is deemed to be ‘screen detected’. Women can, however, attend before or after their actual invitation date as they have to make their own arrangements for the test to be carried out. A cut-off point of six months is therefore used to decide whether a woman had a smear as a result of receiving or expecting an invitation for screening or because of symptoms. This was chosen as the call and recall system continues to send reminder letters to a woman for up to six months after the invitation is due using the nonresponder and final non-responder system. Thus, if a woman who was on routine recall attended within six months of her invitation date (early or late), the referral smear is classified as routine and the invasive cancer was therefore ‘screen detected’. If the cancer diagnosis occurred more than six months after the date that the referral smear was taken, the ‘screening status’ of the cancer is ‘screen detected delayed’. If a woman had a smear recommending referral up to six months before her next invitation date and was then diagnosed with cervical cancer, the smear is assumed to be symptomatic and is excluded, and the ‘screening status’ of the cancer is ‘interval’ as it was diagnosed in the time interval between routine smears. If a woman was diagnosed with cancer up to six months after her next invitation date, but had not actually attended for screening, the cancer also has a ‘screening status’ of ‘interval’. This is because although the woman had not attended for screening, it is assumed that she could have attended any time up to six months after her next invitation date. Only after this time period would the cancer be classified as a ‘lapsed attender’. If a woman had a smear recommending referral more than six months after her invitation date and was then diagnosed with cervical cancer, the smear is excluded as it is assumed to be symptomatic, and the ‘screening status’ of the cancer is ‘lapsed’ as it was diagnosed in a woman who had not attended her last routine invitation at the recommended time interval. The same criteria apply to women who had a smear recommending referral while on early recall following a negative, inadequate or low-grade abnormal smear. However, instead of the six-month rule, the time period used is shorter and depends on the woman’s recall interval as shown in Table 2. Cancers diagnosed in women on early recall who did not attend for screening up to the specified number of months after their invitation date, or who did attend but at a later date, have a ‘screening status’ of ‘default’ rather than ‘lapsed’ as the woman defaulted from her designated early recall care programme. When the last smear before diagnosis recommended routine recall or an early repeat, it is automatically included regardless of the recommended number of months between this smear and the previous one because the last smear did not lead directly to referral and diagnosis. The timeline is then used in the same way as previously to determine the ‘screening status’ of the cancer at the point of diagnosis. In the event that a woman had a series of consecutive smears recommending referral, the first of the series is used as the referring smear and all subsequent smears recommending referral are excluded. All hospital gynaecology department smears are automatically excluded, regardless of the result, as they did not occur in response to a screening invitation. If a woman who is eligible for screening did not attend any routine smears, the screening status of the cancer is www.jmedscreen.com
www.jmedscreen.com
3 months
3 months
Smear would not be included because taken too early before next due date (>3 mths early).
3 months
9 months
Journal of Medical Screening
2006
+12 months: due for repeat smear
Default (including where no smear was taken: assumed to be diagnosed due to symptoms)
Do not include smear as taken late(>3 mths late).
More than 1 year 3 months
Lapsed (including where no smear was taken: assumed to be diagnosed due to symptoms)
If no smear was taken but diagnosed due to signs and symptoms. Interval
Date of diagnosis >6 mths later: SDD.
Date of diagnosis 6 mths late).
3 months
If no smear was taken but diagnosed due to signs and symptoms Interval
Date of diagnosis >6 mths later: SDD.
Include smear as taken at correct time.
+ 36 mths: due for routine smear
6 months
Date of diagnosis 6 mths early).
1 year
Last smear was a repeat (R) code (could be negative, inadequate or low grade but not a routine (A) or referring (S) action code). Next smear (if a smear was taken) is a referring smear that leads to diagnosis
TimelineTwo
Screening status:
Smear routine?
Day 0: Last smear (recommending 36 months routine recall)
Time period:
Timeline One Last smear was negative recommending routine repeat after 36 months (2A36). Same time line for women on 60 months repeat but interval cancers would go up to 4 years 6 months. Next smear (if a smear was taken) is a suspend code that leads to diagnosis and referral.
Smears not recommending referral are included in the analysis regardless of time intervals as they have not lead to referral and diagnosis.
Classification of invasive cervical cancer screening histories 139
Volume 13
Number 3
140
Bagnall et al.
Table1 WM classification system ‘screening status’ at diagnosis categories for invasive cervical cancers Abbreviation
Category
Definition
SD
Screen detected
SDD
Screen detected delayed
I
Interval
LP
Lapsed
D
Default
NA
Non-attender
NE
Not eligible
DBI
Diagnosed before first invitation
Diagnosed after having a routine smear that resulted in a suspend code and with referral and diagnosis within six months of the smear Diagnosed after having a routine smear that resulted in a suspend code and with referral and diagnosis occurring more than six months after the smear was taken Date of diagnosis is before the woman is due to attend for her next screen based on the recall interval of her last screen and the cut-off periods identified in the timelines in Table 2 Woman has attended for screening in the past, but did not attend in response to her last routine screening invitation (which was a normal recall after a negative smear) Woman has attended for screening in the past but did not attend in response to her last invitation (which was an early recall after a negative, inadequate or low-grade smear) Woman was eligible for screening at the time of diagnosis but has never attended for a screening smear Woman was aged 65 or over at the time of diagnosis and was therefore outside the age band for routine screening Diagnosed before 20th birthday or within six months after 20th birthday and has not had a smear within this period
Table 2 Cut-off points used when deriving a ‘screening status’ for women on normal and early recall intervals Recall interval
Cut-off point
3, 4 or 5 years
Should attend 76 months from the date that the next smear is due Should attend 73 months from the date that the next smear is due Should attend within 1 and +3 months from the date that the next smear is due Cannot attend early, but can attend up to 3 months late
6 or 12 months 2 or 3 months 1 month
‘non-attender’. This applies to all women over the age of 20.5 years who had only a single smear recommending referral. If the woman was diagnosed with cervical cancer before her 20th birthday or up to six months after this date and did not have a smear within this period, the screening status of the cancer is ‘diagnosed before first invitation’. If the woman was diagnosed after her 65th birthday, the screening status is ‘not eligible’ for invitation to routine screening. Depending on her age and the date of diagnosis, a woman in this category may or may not have been eligible for cervical screening in the past and her cancer may or may not have a ‘screening history’ classification.
Derivation of ‘screening history’category Once a ‘screening status’ at diagnosis has been assigned to each invasive cervical cancer, a flow chart based on the answers to five simple questions is used to classify the results of previous screening tests and thus to obtain a ‘screening history’ category to accompany the ‘screening status’ category. The system divides the ‘screening history’ component into five parts, each of which is classified using a series of numerical options which are combined to give a five figure classification (see Figure 2). Part One examines whether the woman has a screening history, and, if not, why (e.g. because she was diagnosed before her 20th birthday). Where women did not attend for screening, the ‘screening history’ subclassifications correspond directly with the ‘screening status’ categories of ‘non-attender’, ‘diagnosed before first invitation’ and ‘not eligible’. Part Two examines, for all invasive cancers in women who had at least one cervical smear, the length of time between the diagnosis of the invasive cervical cancer and the last Journal of Medical Screening
2006
Volume 13
Number 3
screening test. Part Three examines the cytology grade and recommended recall interval from the last smear (e.g. a lowgrade abnormal smear recommending early recall). Part Four examines whether the woman was ever referred to colposcopy (suspended from screening in the past) and, if so, how long ago this occurred. Part Five examines the reason for a woman having been referred to colposcopy in the past (three inadequate smears, persistent mild or borderline [low grade] smears, a high-grade smear [moderate or severe dyskaryosis or worse] or referred on a negative smear). It also examines the results of previous smears for women who were never referred in the past (no previous screening, negative smears only, inadequate smear(s) not recommending referral or low-grade abnormal smear(s) not recommending referral). The ability of the ‘screening status’ and ‘screening history’ components of the new classification system to adequately classify invasive cervical cancers and to provide the diagnostic route data item required for the NCDS was then compared with that of the ABC One and NCN classification systems. All cases of invasive cervical cancer diagnosed in the WM in the four most recent years available (2000–2003) that had been assigned a ‘screening status’ were included in the analysis (n ¼ 820).
RESULTS Derivation of the ‘diagnostic route’ data item for the NCDS Figure 3 shows how each of the categories in the ABC One and NCN systems map to the four ‘diagnostic route’ categories required for the NCDS and to the eight ‘screening status’ classifications derived using the new WM system. As the ABC One system deliberately excludes all smears taken within six months of the diagnosis of an invasive cervical cancer, it cannot be used to reliably identify cancers diagnosed as a consequence of an attendance for screening (‘screen detected’). Figure 3 shows that a ‘screen detected’ cancer could be present within ABC One categories 3, 4 and 5 if a woman with an invasive cervical cancer had negative, abnormal or inadequate smears in the preceding 0.5–5 years or any previous treatment for CIN. In general, cancers detected in women who had only one smear cannot appear in ABC One categories 1 and 2, as all smears taken within six months of diagnosis are excluded. The only exceptions are a very small number of cancers classified by the WM www.jmedscreen.com
Classification of invasive cervical cancer screening histories
141
Figure 2 Flow chart used to assign a ‘screening history’ category to each invasive cervical cancer
system as ‘screen detected’ cancers, where the diagnosis date is within six months of a woman’s first and only smear (category 1) or within six months of a routine five-year recall smear (category 2). An ‘interval’ cancer can similarly be present within ABC One categories 3, 4 and 5 but not within categories 1 and 2. The only ABC One category that corresponds directly to an NCDS diagnostic route category or to the WM system is category 6 (abnormal smears www.jmedscreen.com
recommending referral with subsequent delay in diagnosis), which is equivalent to ‘screen detected delayed’ in the WM system and ‘screen detected’ in the NCDS classification. The NCN system also deliberately excludes all smears taken within six months of the diagnosis of an invasive cervical cancer, and therefore cannot be used to reliably identify screen-detected cancers. ‘Screen detected’ and ‘interval’ cancers could be present in NCN categories 3, 4 Journal of Medical Screening
2006
Volume 13
Number 3
Journal of Medical Screening
2006
1, 2 or 3
Volume 13
Number 3
No
No* Yes (ABC One) No (NCN)
No*
LP
NA
DBI
Interval
Default
Lapsed
Non attender
Diagnosed before first invitation
Above eligible age in 1988
Aged 65+ at diagnosis
2
3
3
3
3
3
3
1, 2 or 3
1
No
No
Yes (but if had smears within 6 months two negative smears >6 months later later
Previous treatment for Abnormal smears CIN after abnormal recommending referral smears recommending with subsequent delay referral in diagnosis
Figure 3 Ability of the ABC One and NCN classification systems to complete the diagnostic route data item required for the National Cancer Data Set
Definitions in the National Cancer Data Set 'diagnostic route' data item 1 Cancers detected by the screening programme 2 Interval cancers occurring in patients screened by a national screening programme 3 Other cancers 9 Not known (default)
# ABC One and NCN categories 1−6 are not exactly equivalent, but the pairings used are appropriate for the purposes of this table Yes* Dependent on recall interval (could be lapsed / interval / normal recall) No* Could include a very small number of SD cancers with a diagnosis date within 6 months of a single smear (category 1) or within 6 months of a routine 5 year recall smear (category 2)
NE
D
I No
Yes*
No*
No*
Yes*
Screen detected (diagnosis > 6 months later)
No*
1
3
All negative smears, most recent taken in preceding 0.5-5 years
No*
SDD
1, 2 or 3
Abnormal/inadequate Negative smear(s) in smear(s) in preceding preceding 0.5 − 5 years 0.5 − 5 years
SD (3 yr recall) Screen detected SD (4 or 5 yr recall)
2
All negative smears, most recent taken more than 5 years ago
Screened > 5 years before diagnosis
1
No history
No smears taken
1
NCN#
ABC One#
3
NHSCSP ABC One and NCN categories exclude all smears taken within 6 months of diagnosis and only classify smears in women aged 20 − 64
3
Screening status classification
Equivalent NCDS 'diagnostic route' category
142 Bagnall et al.
www.jmedscreen.com
Classification of invasive cervical cancer screening histories
143
and 5 if a woman had all negative smears within the last 0.5–5 years, a borderline or mild smear followed by two negative smears or a diagnosis of cancer within six months, or a cytology warranting colposcopy followed by two negative smears. As with the ABC One system, cancers detected in women who had only one smear generally cannot appear in NCN categories 1 and 2, as all smears taken within six months of diagnosis are excluded and ‘interval’ cancers can be present within NCN categories 3, 4 and 5, but not within categories 1 and 2. The only NCN category that corresponds directly to an NCDS diagnostic route category or to the WM system is category 6 (cytology warranting colposcopy followed by diagnosis >6 months later) which is equivalent to ‘screen detected delayed’ in the WM system and ‘screen detected’ in the NCDS classification. Table 3 shows for the 820 invasive cervical cancers diagnosed in the WM region in 2000–03 in women who were eligible for cervical screening at the time of diagnosis, how the ‘screening status’ category obtained using the WM system would change if the NCN definitions were applied. In the NCN system, as with the ABC One system, all smears taken within six months of the diagnosis of the invasive
Table 3 Changes in the ‘screening status’ categories derived by applying the NCN criteria to the new WM classification system Reclassified ‘screening status’ using NCN criteria
WM system ‘Screening status’
No.
SD
SDD
SD SDD I D LP NA
193 55 129 66 227 150
0 0 0 0 0 0
3 55 3 9 19 11
2 0 95 0 0 0
36 0 7 44 0 0
150 0 23 9 208 0
2 0 1 4 0 139
Total
820
0
100
97
87
390
146
I
D
LP
NA
cervical cancer are deliberately excluded. In addition, the NCN system ignores all inadequate smears within the whole screening history and includes all smears taken more than six months prior to diagnosis regardless of whether they are taken as a result of the screening programme or in response to symptoms. As a result, none of the cases in the cohort can be identified as ‘screen detected’ using the NCN system. Of the original 193 ‘screen detected’ cancers identified by the WM system 150 would be classified as ‘lapsed’, 36 would be ‘default’ and two would be ‘interval’ if the NCN criteria are applied. Only three cancers would still be identified as ‘screen detected’ but these would appear as ‘screen detected delayed’. Two cases would become cancers in a ‘nonattender’. Generally speaking, the change from ‘screen detected’ to ‘lapsed’ or ‘default’ is due to the exclusion by the NCN system of the smear taken within six months of the cancer diagnosis. In those cases that have changed to ‘lapsed’, the woman was on routine recall and attended at the appropriate time interval for her next smear, but this smear is excluded in the NCN system, making the woman appear ‘lapsed’. The women who are reclassified as ‘interval’ had a smear taken within six months of diagnosis which was excluded, but whose cancer was still diagnosed before the maximum time that could elapse before their next smear was due. Table 3 also shows that, after applying the NCN system definitions, of the original 129 ‘interval’ cancers classified through the WM system, 23 would be reclassified in the ‘lapsed’ category and a further seven would move to the ‘default’ category. Importantly, as the NCN system does not take into consideration the recall code and number of months recall that an individual woman is on, it would not normally be possible in this system to distinguish between ‘interval’, ‘lapsed’ and ‘default’ ‘screening history’ categories. These cases have, however, been included in Table 3 for information. Clearly, changes from a ‘screen detected’ cancer to an ‘interval’ cancer and from a ‘screen detected’ or ‘interval’ cancer to a cancer in a ‘defaulter’ or a
Table 4 The most frequently occurring screening histories diagnosed in 2000–2003 in women eligible for screening and their derivation using the screening histories flow chart classification system ‘Screening history’ classification showing part of flow chart used to provide each component One
Two
Three
Four
Five
1 0
– 2
– 1
– 1
– 2
0
1
5
1
4
0
1
5
1
2
0
3
1
1
2
0
2
1
1
4
Subtotal Total of all other categories Grand total
www.jmedscreen.com
% of women (aged 20–64 years)
‘Screening history’ definition
No.
Woman was eligible but did not attend for screening Last smear was negative taken 0.5–5 years before diagnosis, the woman has all smears in history negative and has never had a referring smear in history Diagnosed within six months of a referring smear (taken at the recommended time interval after the previous smear), the woman has low-grade abnormal smear(s) in history but has never had a referring smear in history Diagnosed within six months of a referring smear (taken at the recommended time interval after the previous smear), the woman has all smears in history negative and has never had a referring smear in history Last smear was negative taken 5–10 years before diagnosis, the woman has all smears in history negative and has never had a referring smear in history Last smear was negative taken 0.5–5 years before diagnosis, the woman has low-grade abnormal smear(s) in history but has never had a referring smear in history
150 77
18.29 9.39
70
8.54
65
7.93
57
6.95
37
4.51
456 364
55.61 44.39
820
100.00
Journal of Medical Screening
2006
Volume 13
Number 3
144
Bagnall et al.
‘non-attender’ would be particularly important if the data were to be used to evaluate the efficacy of the NHSCSP.
Use of the flow chart to identify the screening histories of cohorts of women By selecting specific age groups, time periods or geographical areas the ‘screening status’ and ‘screening history’ classifications can be used to examine the distribution of the categories in different cohorts of women and how these distributions change with time. Table 4 shows the six most commonly occurring screening histories for the 820 women diagnosed with invasive cervical cancer in the years 2000–03 who were eligible for screening. The first column shows how these would be classified using the flow chart in Figure 2 starting with Part One at the top of the flow chart. Of the women diagnosed with invasive cervical cancer, 81.71% had attended for screening at some time, with 18.29% of cancers being diagnosed in women who were eligible for screening but who did not attend. In women who had attended for screening, the most common classification (9.39% of all women) was a cancer that was diagnosed symptomatically after all negative smears, with
the last negative smear taken 0.5–5 years before diagnosis. Of all women, 8.54% had a cancer diagnosed within six months of a referring smear (taken at the recommended time interval after the previous smear) and had a low-grade abnormal smear(s) in their history but had never been referred previously for colposcopy. A further 7.93% of all women had a cancer diagnosed within six months of a referring smear (taken at the recommended time interval after the previous smear) with all other smears in their history negative and no previous referral to colposcopy. In 6.95% of all women, the last smear was negative and taken 5–10 years before diagnosis, with all smears in their history negative and with no previous referral to colposcopy. A further 4.51% of all women had a cancer that was diagnosed symptomatically with low-grade abnormal smear(s) in their history but no previous referral for colposcopy.
Use of the WM system to identify cohorts of women of particular interest to the NHSCSP By using the ‘screening status’ and ‘screening history’ classification systems alone or in combination, cohorts of
Table 5 Examples of ‘screening status’ and ‘screening history’ classifications of particular interest for monitoring the effectiveness of the NHSCSP and their derivation using the WM classification system ‘Screening status’ and ‘screening history’ definitions
Example
Potential problem
One
Interval A higher than average proportion of interval cancers occurring after a negative normal recall smear before a woman is due to attend for next smear suggesting the possibility that abnormal smears have been misinterpreted by the screening laboratory
Screening status: interval Screening history: last smear result was negative normal routine recall taken o5 years before diagnosis and the woman has had either no previous smears or only previous negative smears
Two
Previous low-grade smear(s)
Screening status: any apart from non-attender, not eligible and diagnosed before first invitation Screening history: Smear of any grade taken o5 years before diagnosis and the woman has had low-grade smears but was never referred for colposcopy
A higher than average proportion of women who have had low grade smears in their screening history which could suggest that smears may have been under-reported by the screening laboratory Three
Previous referral
A higher than average proportion of women who have been referred for colposcopy less than five years before they were diagnosed with cancer which could suggest that there may have been problems with the colposcopy examination and/or the taking and/or reading of biopsies/histology (assuming that the woman did attend for colposcopy when invited)
Screening status: any apart from non-attender, not eligible and diagnosed before first invitation Screening history: Smear of any grade taken o5 years before diagnosis and the woman has been referred for colposcopy (for any reason) o5 years before the diagnosis of the cancer
‘Screening history’ classification showing part of flowchart used to provide each component One
Two
Three
Four
Five
No.
0
1 or 2
1
1
1 or 2
61
0
1 or 2
*
1
4
147
0
1 or 2
*
2 or 3
*
22
*Any of the flow chart codes can be used
Journal of Medical Screening
2006
Volume 13
Number 3
www.jmedscreen.com
Classification of invasive cervical cancer screening histories
145
Table 6 Changes in the ‘screening status’ categories derived by applying the NCN criteria to the three cohorts of women identified in Table 5 Cohort
‘Screening status’ classification
Classification using the WM system Example No. SD SDD One 61 0 0 Two 147 71 18 Three 22 8 5
I 61 28 7
D 0 12 1
LP 0 18 1
NA 0 0 0
Total
96
13
19
0
230
79
Classification using the NCN Example No. SD One 61 0 Two 147 0 Three 22 0 Total
230
0
23 criteria SDD 0 20 11 31
with the WM system I D LP 49 0 12 25 43 59 2 7 2 76
50
73
NA 0 0 0 0
women with screening histories of particular interest to those monitoring the efficacy of the NHSCSP can easily be identified for further analysis and audit. Examples of three such screening history cohorts and their derivations using the WM screening history flow chart are shown in Table 5. Table 6 shows the ‘screening status’ categories of the cases included in each cohort and how these would change if the criteria used in the NCN system were used to assign the WM categories. Example One in Table 5 uses both the ‘screening status’ and ‘screening history’ classifications to identify 61 women who were diagnosed with an ‘interval’ cancer following a routine negative normal recall smear and have no smears, or only negative smears in their screening history. If a particular laboratory has a high proportion of women with this combination of ‘screening status’ and ‘screening history’, it could suggest that an unusually high number of abnormal smears may have been reported as negative and that a detailed audit of the cases should be undertaken to ascertain if this was the case. This particular cohort of women could not be identified using the NCN system as, with previous negative smears, they would fit into screening status classification 2 or 3 in Figure 3 and would thus not be distinguished from women who did have a referring smear (who would be classified as ‘screen detected’ rather than ‘interval’ cancers by the WM system). Furthermore, Table 6 shows that if the criteria used in the NCN system were used to derive this cohort of women, only 49 (80%) of the 61 cases would have been included, as 12 would have been classified as ‘lapsed’. Example Two in Table 5 shows how above average proportions of women who have low-grade smears in their screening history can be identified. Table 6 shows that within this cohort there are 18 women (12%) whose ‘screening status’ was ‘lapsed’ and whose cancers may have developed in the time between their last smear and diagnosis. Deriving a ‘screening status’ and a ‘screening history’ category for each case makes it possible to exclude these women and to focus on those who have ‘screen detected’ and ‘screen detected delayed’ cancers. There were also 12 women (8%) whose ‘screening status’ was ‘default’, indicating that they failed to attend for an early recall smear. The NCN system does not allow the identification of all women in this cohort as women who had their low-grade abnormal smear within six months of diagnosis and those who also had cytology warranting colposcopy more than six months before date of diagnosis would be excluded.
www.jmedscreen.com
Furthermore, Table 6 shows that if the criteria used in the NCN system were applied to this cohort of women, 59 (40% rather than 12%) would have been classified as ‘lapsed’ and 43 (29% rather than 8%) as ‘default’. Data on women who have in the past been referred for assessment as a result of screening can also provide information on colposcopy services. Example Three in Table 5 includes all women who were referred for colposcopy, for any reason, within five years of their cancer diagnosis. Using the NCN system, this cohort would be much smaller, as this classification system only uses the most recent episode of cytology warranting colposcopy and would also not include women referred to colposcopy because of three inadequate smears. Women in this category are an important subgroup, as the reason for the delay in diagnosis may reflect service quality issues such as an extended period of investigation, failure to diagnose the disease or long waiting times. Alternatively, the delay may be due to complications caused by concurrent medical conditions, pregnancy or the woman’s choice of investigations and management. Table 6 shows that if the criteria used in the NCN system were applied to this cohort of women, nine (41%) of the 22 cases would have been classified as ‘default’ or ‘lapsed’ rather than only two cases (9%) with the result that problems in service provision leading to the delayed diagnosis may have been overlooked.
DISCUSSION Although the aim of the NHSCSP is to detect changes in the cells of the cervix that may lead to cancer in the future, it is important to identify invasive cancers that have been detected as a result of a screening test (‘screen detected’) and in the time interval between routine screening invitations (‘interval’ cancers) in order to understand more about the type of cancers that are not being prevented by the NHSCSP and the populations of women in which they occur. When this information is combined with data on a woman’s screening history and the stage at diagnosis of her cancer, it can also provide a valuable insight into the quality of screening programmes. There will, for example, be more concern about a programme with a relatively large number of late stage ‘screen detected’ and/or ‘interval’ cancers than one with a relatively small number of micro-invasive, earlystage cancers. Similarly, there will be less concern about laboratory and colposcopy services in a primary care trust (PCT) where a high proportion of invasive cancers occur in women who have failed to attend for routine screening (‘lapsed’ or ‘non-attender’ cancers) or an early recall invitation (‘default’ cancers), but it may nevertheless be important to examine the quality of the health promotion or fail-safe activities undertaken by the PCT. An important feature of the new WM classification system is the ability to combine independent information on a woman’s interaction with the NHSCSP (her ‘screening status’) and the results of her smear tests (her ‘screening history’) to identify cohorts of women of particular interest to quality assurance services. Thus, as illustrated in Table 5, the ‘screening history’ component can be used to identify a group of women with a history of low-grade smears prior to the diagnosis of their invasive cancer. The ‘screening status’ component then provides the information required to distinguish between the 117 cancers diagnosed in women who did attend for routine screening (‘screen detected’, ‘screen detected delayed’ and ‘interval’) and those cancers in the 30 women who failed to attend either a routine screen (‘lapsed’) or an early recall invitation (‘default’) prior Journal of Medical Screening
2006
Volume 13
Number 3
146
Bagnall et al.
to their diagnosis. In the first three groups, it is possible that the low-grade abnormal changes that were present in previous smears may have been under-reported by the screening laboratory, and in the ‘lapsed’ and ‘default’ groups, it is possible that the cancer would have been detected at an earlier, possibly non-invasive stage had the women attended in response to their most recent routine or early recall invitation. The flexibility of the new WM classification system means that cancers can be allocated a consistent ‘screening status’ and ‘screening history’ regardless of when a woman was diagnosed with cancer, even when local recall interval policies have changed over time. In order to classify a cancer, the WM system examines the date and result code of every screen in a woman’s screening history, together with information on the generation of invitation letters held on the national call and recall system. It also enables completion of a full cytology history regardless of whether the woman has moved. This ensures that the diagnosing hospital service has full information, even if the tests were not reported within their organization. The classification of women on an individual basis means that changes in recall interval policy and differences in referral pathways can be taken into account for each woman and this negates the need for a referral ‘points system’ as used in the NCN system. It also means that the classification system is robust enough to cope with changes in the NHSCSP such as the recent standardization of the recall interval to three years for women aged 25–49 years and five years for women aged 50–64 years, and the increase in age at first screen to 25 years.7 One of the main differences between the WM system and the NCN and ABC One systems is that the ‘screening history’ categories are not limited to a predefined list, but consist of a combination of five numerical scores each representing a different aspect (or part) of the woman’s screening history. Anonymized data analyses can be carried out as required on cohorts of cancers confined to an individual category in one part of the classification system or a cohort derived using all five parts of the classification. Another difference is that the WM system does not exclude inadequate smears. As these can lead to or delay referral to colposcopy, this will be valuable in future, as it will be possible to compare outcomes for women who have been referred and diagnosed with invasive cervical cancer following three inadequate smears in populations screened by conventional screening and in those screened using liquid-based cytology (LBC) technology. Although the WM system does not include a specific classification for women who have been diagnosed with in situ cervical cancer in their past as does the ABC One system, it does identify women who may have been expected to have attended colposcopy from their ‘screening history’ data and for whom information regarding previously diagnosed CIN III can be routinely obtained from the local cancer registry by the QARC to pass on to local clinical teams and data on CIN I or II and previous colposcopy attendances obtained from the relevant services. This will facilitate the collation of all relevant factors which may have led to a cancer diagnosis which can then be used to supplement the regional classifications and screening history data and assist local clinical teams in obtaining information such as cytology and histology results from other areas which they may not be aware of or have easy access to. An important step in the derivation of a cervical screening history is the identification and exclusion of non-relevant smears. The NCN and ABC One classification systems attempt to achieve this by excluding all smears taken within Journal of Medical Screening
2006
Volume 13
Number 3
six months of the cancer diagnosis to avoid erroneously including symptomatic smears. However, the exclusion of all smears taken within six months of diagnosis has important implications for the quality assurance of screening services, as it means that it is often not possible to distinguish between women who have attended for screening when invited and who have been diagnosed with cervical cancer in the time interval between two screens (‘interval’), and women who did not attend when invited for their last smear (‘lapsed’). The effect of excluding smears taken within six months of diagnosis is illustrated in Table 6 for a cohort of 61 women classified by the WM system as having ‘interval’ cancers. Using the NCN and ABC One systems, only 49 of these cancers would have been identified as ‘interval’ cancers, with 12 (20%) classified as ‘lapsed’, with very different implications for the quality of the local screening service. Unlike the two existing classification systems that try to exclude symptomatic smears, the new WM classification system deliberately tries to identify these smears in order to obtain a ‘screening status’ for each cancer with which to populate the diagnostic route data item in the NCDS. In order to identify symptomatic smears, the WM system makes certain assumptions based on when the individual woman would have been invited for her next screen and whether this corresponds to when she did actually attend. The assumptions made by the WM system do have limitations. Some women with symptoms may, for example, postpone a visit to their general practitioner (GP) until they are invited to attend for screening and, without access to GP records, it is not possible to know when a woman has presented to her GP with symptoms. The assumptions are, however, applicable to the majority of women, leaving only a few very difficult cases where women have a complex series of referral codes or a series of unexplained GP smears at very short intervals where the screening history cannot be classified without a more detailed examination. It is envisaged that the classifications obtained regionally will be routinely passed back to local clinical teams to enable further information on symptom status and previous colposcopy to be obtained. For some cases it may then be necessary to modify the screening history classification to reflect information identified at the multi-disciplinary review. Complex and unusual screening histories have become less common since the publication of ABC One in 19953 and the quality and consistency of the data held on the national call and recall computer system has improved in tandem. Although the WM classification process is relatively time consuming if each individual case is looked up on the call and recall computer system, the improved quality and consistency of the data held on the latter means that, for invasive cervical cancers diagnosed from the late 1990s, it should be possible to automate the allocation process for the majority of cases, leaving only a few cancers with complex histories that require manual intervention.
CONCLUSION This paper has demonstrated how a refinement of two existing screening histories classification systems and the addition of a new ‘screening status’ component can increase the value and consistency of the information that can be derived from routine invasive cervical cancer audits. By allocating to each cancer both a ‘screening status’ and a ‘screening history’, potential issues relevant to cytology, www.jmedscreen.com
Classification of invasive cervical cancer screening histories
histology, colposcopy, call and recall and the woman’s response to invitations can be identified and subjected to further detailed investigation and local audit. Additional information from local clinical teams can also be added. In addition to providing high quality data with which to audit critical aspects of the NHSCSP, the new WM classification system offers QARCs a semi-automated method with which to derive the information required by cancer registries to populate the diagnostic route data item in the NCDS. National adoption of this new screening histories classification system would provide a detailed, consistent, nationally comparable cytology screening history for all invasive cervical cancers which could be used in the national and regional evaluation of the NHSCSP, and in local audit by clinical teams, supplemented by histology and colposcopy data. In addition, the derived classification can be collapsed down to provide the diagnostic route data item required for the NCDS.
................
Authors’ affiliations Ms Helen Bagnall, Cervical Screening QA Research & Information Manager, Cervical Screening QA Reference Centre, West Midlands Cancer Intelligence Unit, The University of Birmingham, Birmingham, UK Ms Philippa Pearmain, Deputy Regional Director of Cervical Screening QA, Cervical Screening QA Reference Centre, West
www.jmedscreen.com
147 Midlands Cancer Intelligence Unit, The University of Birmingham, Birmingham, UK Ms Joanne Clare, Cervical Screening QA Information Assistant, Cervical Screening QA Reference Centre, West Midlands Cancer Intelligence Unit, The University of Birmingham, Birmingham, UK Dr Gill Lawrence, Regional Director of Breast & Cervical Screening QA, Cervical Screening QA Reference Centre, West Midlands Cancer Intelligence Unit, The University of Birmingham, UK
REFERENCES 1 2 3 4 5 6 7
Adam S. Epinet Notification CEM/CMO/2001/6, Department of Health, 3 May 2001 National Cancer Minimum Dataset Version 4.0. http://www.icservices.nhs. uk/cancer/pages/dataset/docs/dataset.pdf (last accessed 24 August 2005 NHSCSP. Achievable Standards, Benchmarks for Reporting, and Criteria for Evaluating Cervical Cytopathology. NHSCSP Publication No.1. 1st edn. Sheffield: NHSCSP Publications, 1995 Sasieni PD, Cuzick J, Lynch-Farmery E. Estimating the efficiency of screening by auditing smear histories of women with and without cervical cancer. Br J Cancer 1996;73:1001–5 NHAIS Open Exeter website http://www.nhsia.nhs.uk/nhais/pages/products/vaprod/openexe/ (last accessed 24 August 2005 Lawrence G, Kearins O, O’Sullivan E, et al. The West Midlands breast cancer screening status algorithm – methodology and use as an audit tool. J Med Screen 2005;12:179–84 Department of Health Modernising the NHS Cervical Screening Programme, NICE Appraisal of Liquid Based Cytology, Advice to the Service, Department of Health, October 2003. http://www.dh.gov.uk/PublicationsAndStatistics/ Publications/PublicationsPolicyAndGuidance/PublicationsPolicyAndGuidance Article/fs/en?CONTENT_ID ¼ 4081380&chk ¼ V2as5E (last accessed 11 October 2005)
Journal of Medical Screening
2006
Volume 13
Number 3
