DOI: 10.1002/jgf2.168
EDITORIAL
Subclinical cancer diagnosis fallacy Major reasons for overtesting among physicians are considered to
medicine, while 669 participants (71%) worked in hospitals, in which
include the incorrect belief that ordering many tests would identify
77 (8.2%) were those working in university hospitals.
subclinical disease and would always improve prognosis (subclinical
First, many physicians in Japan showed limited knowledge of
diagnosis fallacy), in addition to defensive medicine, lack of access
what evidence might prove that a cancer screening test saves lives.
to previous data, and requests from patients.1 However, our survey
Among Japanese physicians, 40% incorrectly responded that find-
as well as one in the USA showed physicians did not perceive this
ing more cancer cases in screened as opposed to unscreened groups
fallacy as a cause of overtesting.
provided the proof (Table 1). But the higher incorrect response (48%)
In fact, ordering many tests would tend to detect subclinical
was identified in physicians in the US study. 2
disease but would not always improve prognosis. Regarding can-
About half of physicians in Japan incorrectly responded that
cer screening, the detection of subclinical diseases is associated
increased survival data prove that screening saves lives (48%), al-
with greater risk of overtreatment because of the increased bias
though the US physicians did so in much higher incorrect rate (76%).
of lead time and overdiagnosis. But, many physicians seem not to
However, there were only a half of Japanese physicians who cor-
understand the knowledge of subclinical cancer diagnosis fallacy
rectly responded mortality data provide this proof, compared to
and such physicians might not recognize this as a potential reason
those (81%) in the USA. Thus, many physicians could not distinguish
for overtesting.
between incorrect evidence for screening (increased survival) and
A nationwide survey was conducted to evaluate the knowledge
correct evidence (lower cancer mortality) in both Japan and the USA.
about cancer screening tests and subclinical cancer diagnosis fal-
Next, physicians in Japan were also more likely to report they
lacy in cancer screening, based on a questionnaire developed in the
would definitely recommend the screening test that improved 5-year
previous study by Gigerenzer et al. 2 Our hypothesis was that there
survival compared with the one that lowered cancer mortality (21%
would be many physicians with lack of this knowledge. Thus, physi-
vs 3%). Both proportions among Japanese physicians were much
cians would tend to perceive that subclinical cancer diagnosis fallacy
lower than those among physicians in the USA (69% vs 23%) and this
is not recognized as important reason for overtesting.
trend might reflect there would be lower involvement with cancer
Participants in our survey included physicians of primary care,
screening among Japanese physicians compared with American.
general medicine, or specialty throughout Japan. They were volun-
Third, regarding the test that improved 5-year survival, physi-
tarily invited through members of an online educational community
cians received additional information that screening test increased
(M-Three) in January 2018. The sponsor for this community had no
the proportion of cancer cases detected at stage I (from 36% with-
role in design and data analysis of the survey. The participant was
out screening to 54% with screening) and they were asked how
involved with obtaining a point gift for the online community.
to change their behavior about the recommendation to patients.
In a total of 940 participants, there were 864 (92%) men and
Although this information provides no support for the screening test
851 (91%) physicians with at least 10 years of clinical experience.
as early-stage cancer can be detected more by a harmful screening,
In all participants, 79% were physicians of primary care or general
47% of Japanese physicians (68% of American physicians) responded
Item 1
Item 2
Item 3
Proves
376
40.0%
451
48.0%
466
49.6%
Does not prove
374
39.8%
286
30.4%
234
24.9%
Does not know
190
20.2%
203
21.6%
240
25.5%
TA B L E 1 Understanding among Japanese physicians about evidence that cancer screening saves life (N = 940)
Item 1: More cancers are detected in screened populations than in unscreened populations (correct answer: does not prove). Item 2: Screen-detected cancers have better 5-year survival rates than cancers detected because of symptoms (correct answer: does not prove). Item 3: Mortality rates are lower among screened persons than unscreened persons in a randomized trial (correct answer: proves).
© 2018 The Authors. Journal of General and Family Medicine published by John Wiley & Sons Australia, Ltd on behalf of Japan Primary Care Association. 70 | wileyonlinelibrary.com/journal/jgf2
J Gen Fam Med. 2018;19:70–71.
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71
EDITORIAL
that this information made them more or much more likely to recommend the screening. For the test that reduced mortality, physicians received additional information that the screening test increased cancer incidence
C O N FL I C T O F I N T E R E S T The authors have stated explicitly that there are no conflicts of interest in connection with this article. Mano Soshi BM1
(from 27 to 46 per 1000 persons over 5 years) and they were also
Takahiro Mizuta BM2
asked how to change their behavior about the recommendation to
Yasuharu Tokuda MD3
patients. Among Japanese physicians, 28% responded the increased
1
incidence made them “more” or “much more” likely to recommend the test, while 62% of American physicians responded so. Based on our results combined with the previous study by
2 3
Faculty of Medicine, Osaka Medical College, Osaka, Japan
Faculty of Medicine, Okayama University, Okayama, Japan
Muribushi Project for Okinawa Residency Programs, Okinawa, Japan Email:
[email protected]
Gigerenzer et al, many physicians interpreted incorrectly higher survival and increased detection with screening tests as proof that the test saves lives. Some physicians incorrectly believed subclinical diagnosis fallacy that greater detection of early-stage cancer or increased incidence in screened groups constitutes evidence of the benefit of screening. Physicians are likely to perceive that subclinical cancer diagnosis fallacy is not recognized as important reason for overtesting. Japanese physicians seemed to be less likely to make a strong recommendation for screening tests even they believed it would be life-saving compared with American physicians. Educational efforts, such as choosing wisely campaign, are needed to improve understanding of screening evidence and subclinical cancer diagnosis fallacy among physicians not only in the USA but also in Japan.3
REFERENCES 1. Greenberg J, Green JB. Over-testing: why more is not better. Am J Med 2013;127:362–3. 2. Wegwarth O, Schwartz LM, Woloshin S, Gaissmaier W, Gigerenzer G. Do physicians understand cancer screening statistics? A national survey of primary care physicians in the United States. Ann Intern Med. 2012;156:340–9. 3. Tokuda Y. Current status of choosing wisely in Japan. J Gen Fam Med. 2015;16:3–4.
