Nasopharyngeal carcinoma (NPC) is one of the most common cancers in Malaysia, a country in Southeast Asia with a multiracial population.
Cancer Causesand Control, 3,
179-182
BRIEF REPORT
Descriptive epidemiology of naso.P liar.Y n g eal in . carcinoma . Peninsular Malaysia
Umapati Prasad and Lekhraj Rampal
(Received 25 November 1991; accepted in revised form 2 January 1992) Nasopharyngeal carcinoma (NPC) is one of the most common cancers in Malaysia, a country in Southeast Asia with a multiracial population. While hospital-based data on NPC and data from a few states have been reported, a comprehensive study involving every known NPC patient in the whole of Peninsular Malaysia in one particular year had never been done. In the present study, the computed incidence rate was not only adjusted for age, sex, ethnicity, and place of residence, but also direct standardization methods of Rothman and Dever were used to reduce any distortion. The mean age of the 365 new cases of NPC registered in 1988 was 46.8 years (SD + 12.2 years). The ages of patients ranged from 10 to 80 years. The incidence in both sexes rose after the age of 20-29 years and reached a plateau between 40 and 49 years. No further rise was exhibited after age 60 years. The Chinese had the highest age-adjusted incidence rates, particularly for the age group 40-49 years, where the incidence rate was 40.1 per 100,000 for males and 14.9 for females. The average ageadjusted male/female ratio was 2.8:1. Age-adjusted incidence varied by place of residence. The pattern that emerged from the data indicated the possibility of interaction between genetic susceptibility and environmental cofactors in the etiology of NPC.
Key words: Incidence rates, nasopharyngeal carcinoma, Malaysia.
Introduction Malaysia, located in southeast Asia, is divided by the South China sea into two main parts, the West and the East (Figure 1). The West, also called Peninsular Malaysia, is situated between Thailand and Singapore, with Thailand above and Singapore below, at 1° to 6°N latitude and between 100° and 104°E longitude. It is
divided further into 11 states. East Malaysia is comprised of two states, Sabah and Sarawak. The total population of Peninsular Malaysia is 11,442,086, with the ethnic distribution being 55.3 percent Malays, 33.8 percent Chinese, 10.2 percent Indians, and 0.7 percent others.
Dr Prasad is with the Department of Otorhinolaryngology, University of Malaya. Dr Rampal is at the Institute of Public Health, Ministry of Health, Kuala Lumpur. Address correspondence to Prof. Prasad, Department of Otorhinolaryngology, University Hospital, 59100 Kuala Lumpur, Malaysia. This study was supported by grant from the Research and Development Unit of the Ministry of Science Technology and Environment, Government of Malaysia. © 1992 Rapid Communications of Oxford Ltd
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U. Prasad and L. Rarnpal
Materials and methods
|lusted Incidence Rate/
Population
~
6-,0 11 - 15
[~
~6 and above,
All histologically confirmed cases of NPC diagnosed between 1 January 1988 and 31 December 1988, from multiple centers within Peninsular Malaysia, were included in this study. All cases that were first histologically confirmed in 1987 but registered for treatment in 1988 were excluded; however, those cases treated in 1989 but first histologically confirmed in 1988 were included. Those patients whose permanent residence was outside Peninsular Malaysia were excluded from the study.
Data collection and a n a l y s i s
Figure 1. (A) Map of Peninsular Malaysia showing ageadjusted incidence rate per 100,000 population according to states. (B) Shows the location of Malaysia with other nations in Southeast Asia. While, in most countries, nasopharyngeal carcinoma (NPC) is relatively rare, with an age-adjusted incidence rate of one per 100,000 population, ~it is one of the most common cancers affecting the people in South China, Taiwan, 2Hong Kong, Singapore, ~and Malaysia. In the absence of an adequate cancer registry in Malaysia, estimates of NPC incidence have been based largely on the relative frequencies of patients seen at major treatment hospitals or on biopsy studies. Armstrong et al4 reported on the age-adjusted incidence of N P C but it was limited to only one of the 11 states, and for the others it was a crude estimate. Reports from the States of Sabah 5 and Sarawak 6 in the eastern part of Malaysia lacked details. In the present study, effort was made not only to include all histologically confirmed N P C cases in the entire area of Peninsular Malaysia within one year (1988), but also to analyze the data in detail adjusting them to the standard World population, to determine the actual incidence rate, and to relate the observations to possible etiologic factors in the development of this cancer. 180
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The data for this study were collected by an ENT surgeon, an epidemiologist, and a research assistant. A standardized format was used to obtain information on age, sex, ethnicity, place of residence, occupation, family history of NPC, date of first histologic confirmation of NPC, type of N P C and the stage, and other variables. In computing the frequency of NPC in Peninsular Malaysia, the incidence rate was based on the number of individuals in the total population who were diagnosed with N P C during a one-year period of observation. The computed incidence rate was considered as a minimum incidence rate in Peninsular Malaysia. To examine whether the occurrence of NPC varied from one age group to another, the population was divided into subgroups, and the age-specific incidence rate was computed. The incidence rate was adjusted for age and sex using the standard World population in 1985. To reduce any distortion caused by the confounding effect of age, sex, and ethnicity, direct standardization methods as described by Rothman 7 and Dever 8were used when the data were examined for the occurrence of N P C by sex and ethnic group.
Results There were 365 new cases (approximately one new case of NPC per day), for analysis. Males constituted 74 percent of the total number of cases. The male : female ratio of the N P C cases was 2.8:1. The age-group ranged from 10 years to 80 years. The mean age of the patients was 46.8 years with a standard deviation of 12.2 years. There were only three (0.8 percent) cases below the age of 20. The youngest patient was a 10year-old male who belonged to the ethnic Malay group. Of the 365 patients with NPC, 315 (86.3 percent) were of Chinese ethnic origin, 47 (12.9 percent) were Malays, and three (0.8 percent) were Indian. The total number of cases rose from 25 below the age of 30 years to 77 at ages 30-39, an increase of 21.1 percent,
Nasopharyngeal cancer in Malaysia Table 1. Age-specific incidence rate (IR) per 100,000 population by sex, Peninsular Malaysia, 1988 Age group
Males
Females
(0.0).
No. of cases
IR
No. of cases
IR
10-29 30-39 40-49 50-59 60+
20 56 100 58 38
0.8 6.4 17.4 15.2 9.7
5 21 34 24 11
0.2 2.3 6.1 6.0 2.8
Total
270
4.0
95
1.4
Table 2. Age-specificincidencerate of nasopharyngeal carcinoma (NPC) per 100,000 population by ethnic group and sex, Peninsular Malaysia, 1988 Age
Malay
Indian
Chinese
noted that in males aged 40-49 years, the incidence rate per 100,000 population for the Chinese was very high (40.1) as compared with the Malays (3.7) and Indians
group
M
F
M
F
M
F
10-29 30-39 40-49 50-59 60+
0.4 1.1 3.7 4.5 3.1
0.1 0.4 1.0 0.9 0.7
1.9 16.1 40.1 36.6 25.1
0.7 6.1 14.9 15.8 5.7
0.0 1.0 0.0 0.0 3.6
0.0 0.0 2.0 0.0 0.0
Total
1.0
0.3
10.7
3.9
0.3
0.2
reaching a peak at 40-49 years with the number of cases rising to 134 (36.7 percent of total). There was sharp decline at age 60 years and over (only 47 cases). The majority (80.3 percent) of cases belonged to the 30-59 years age group. The incidence rate of NPC per 100,000 population was found to vary with age, being lower under age 20. The incidence rate was less than one (0.9) for patients below the age of 30. It rose to 4.3 for those at ages 30-39 years, reaching a peak at 40-49 years (11.9), and plateauing at 50-59 years (10.6). There was a decline in the incidence rate (5.9) at age 60 and over. The age-specific incidence rate per 100,000 population (Table 1) varied with age in both sexes, and the occurrence of NPC was higher in males compared with females, in all age groups. A sudden rise in the incidence was noted at the ages 30-39, reaching a peak at ages 40-49 in both sexes. For ages 40-49 years, the incidence rate among males was 17.4 per 100,000 population as compared with 6.1 for females. Table 2 shows the age-specific incidence rate of NPC per 100,000 population by ethnicity and sex, which differed for each ethnic group and within each ethnic group, and varied with age. The age-specific incidence rates were highest for the Chinese, followed by the Malays. The incidence rates for the Indians were lowest regardless of age group. It was
Incidence rates were then adjusted for age (using the standard World population) and analyzed for sex, race, and place of residence. The age-adjusted incidence rate was also higher in males (4.8 per 100,000) compared with females (1.7). The male :female age-adjusted incidence ratio was 2.9:1 The overall age-adjusted incidence rate was 3.2. The age-adjusted incidence rate of NPC per 100,000 population in Peninsular Malaysia, according to the state where the patients resided, indicated that the highest incidence was in the State of Selangor (26.9) followed by Pahang (12.3), Federal Territory of Kuala Lumpur (10.7) and Penang (7.7). These states also have a predominantly Chinese population. The two lowest age-adjusted incidence rates were found in the States of Kelantan (0.8) and Perlis (1.3), which are populated mainly by Malays.
Discussion It was interesting to note that the different ethnic groups (Malay, Chinese, and Indian) who have been living together in the same country for generations had marked differences in the incidence of NPC. The ageadjusted incidence rate per 100,000 population for Chinese was 11.3 for males and 4.1 for females compared with 1.3 for Malay males and 0.3 for Malay females, and only 0.3 for Indian males and 0.2 for Indian females. For the age group 40-49 the age-specific incidence rate for Chinese was very high at 40.1 per 100,000 for males and 14.9 for females. For Malays in the same age group, it was only 3.7 for males and 1.0 for females. Ethnicity in the occurrence of NPC has also been reported in other studies? In Hawaii, the ageadjusted (standard World population) incidence rate for Chinese was 10.3 and 5.1 per 100,000 population for males and females respectively, as compared with 1.0 and 0.9 for male and female Caucasians? A similar pattern was noted in Singapore, where the age-adjusted incidence rate for the Chinese population was 18.7 and 7.1 per 100,000 for males and females, respectively, as compared with 4.8 and 0.6 for Malay males and females, and 0.9 and 0.6 for Indian males and females. The age-adjusted male : female ratios for the Chinese in the present study (2.8:1) does not differ appreciably from the Chinese in Singapore (2.6 : 1). The male preponderance of NPC was also reported from San Francisco, Singapore, Hawaii, Newfoundland, Quebec, and other parts of the world? In comparing the results of this study with those from other studies, it is noted Cancer Causes and Control. Vol 3. 1992
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U. Prasad and L. Rarnpal that the age-adjusted incidence rate per 100,000 population for N P C in Peninsular Malaysia was high in comparison with most of the other countries in the world but was comparable to those of South China, 1 Taiwan, 2 and Singapore? It also was observed that the incidence rate varied with age. It rose after age 20 years and reached a plateau at 40 to 59 years, without exhibiting any further rise in the older age groups. Buell 1°suggested that such a curve was indicative of exposure to carcinogenic agents quite early in life. The absence of a progressive increase in frequency in the older age group suggested reduced exposure or susceptibility with age, and/or exhaustion of susceptible members of the population. This pattern seems to be compatible with interaction of environmental factor/s (e.g., virus) and/or other chemical agents) with genetic susceptibility.
Acknowledgements--For their invaluable assistance and cooperation, the authors wish to acknowledge their sincerest appreciation to: Dr Albert Lim Kok Hooi, Head, Institute of Radiotherapy, Oncology and Nuclear Medicine, General Hospital, Kuala Lumpur, Malaysia; Dr Narashima, Director, Radiotherapy Radionic Centre, Kuala Lumpur; Dr M. A. M. Zaatar, Head of Radiotherapy Department, Mount Miriam Hospital, Penang; Dr Kandiah, Consultant ENT Surgeon Pantai Medical Centre, Kuala Lumpur; and Associate Professor Vijay Kumar Khanijow, Univer-
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sity Hospital Kuala Lumpur. Our special thanks go to Mr Dinakeran, Research Assistant, for assistance in data collection and computer programming.
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