Trends in the Incidence Rates of Nasopharyngeal Carcinoma among Chinese Americans Living in Los Angeles County and the San Francisco Metropolitan Area, 1992–2002

Li-Min Sun1,2, Meira Epplein1,2, Christopher I. Li1,2, Thomas L. Vaughan1,2 and Noel S. Weiss1,2

1 Division of Public Health Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA
2 Department of Epidemiology, University of Washington, Seattle, WA

Reprint requests to Dr. Li-Min Sun, 1100 Fairview Avenue North, M4-C308, P.O. Box 19024, Seattle, WA 98109-1024 (e-mail: lsun{at}fhcrc.org).

Received for publication June 13, 2005. Accepted for publication August 9, 2005.


    ABSTRACT
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 
Nasopharyngeal carcinoma is much more common in Asian countries than in Western countries. However, since the 1980s, nasopharyngeal carcinoma incidence has fallen among both men and women in Hong Kong, and recently a similar trend has also been noted in Singapore. Using data from the Surveillance, Epidemiology, and End Results Program and the US Census, the authors evaluated recent trends in the incidence rates of nasopharyngeal carcinoma among Chinese living in Los Angeles County and in the San Francisco-Oakland (California) metropolitan area. From 1992 to 2002, the rates of nasopharyngeal carcinoma in these two populations decreased in men by 37% (95% confidence interval: –54, –12) but in women by just 1% (95% confidence interval: –40, 64). In Chinese men, the overall decline in incidence was limited primarily to a decline in the rate of type I tumors (differentiated squamous tumors with keratin production). While the reasons underlying the observed patterns of incidence remain to be determined, changes in lifestyle and environment are likely to be contributory factors.

Asian continental ancestry group; incidence; nasopharyngeal neoplasms; trend


Abbreviations: CI, confidence interval; SEER, Surveillance, Epidemiology, and End Results


    INTRODUCTION
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 
Nasopharyngeal carcinoma is a rare malignancy in Western countries (<1 per 100,000 person-years), but it occurs much more frequently in China and Southeast Asia (>20 per 100,000 person-years among southern Chinese) (1Go). Descendants of Chinese who emigrated to Western countries have lower nasopharyngeal carcinoma incidence rates than do Chinese in Asia, but their rates remain higher than those of White populations in Western countries (2Go, 3Go). Thus, the geographic pattern of incidence of nasopharyngeal carcinoma suggests an interaction between genetic and environmental factors.

According to a system developed by the World Health Organization, nasopharyngeal carcinoma is classified into three histologic categories (4Go). Type I represents well to moderately differentiated squamous cell carcinomas with keratin production. Type II includes nonkeratinizing carcinomas. Type III comprises a diverse group of carcinomas, and these lesions often are described as undifferentiated carcinomas or lymphoepitheliomas (4Go). Types II and III are more commonly associated with elevated Epstein-Barr virus titers than is type I (5Go). Types II and III also have a better prognosis than type I has (6Go, 7Go). While the most common type of nasopharyngeal carcinoma among US-born Chinese and Whites is type I tumors, among Chinese who reside in Hong Kong, Taiwan, and Macao, type III tumors predominate.

The incidence of nasopharyngeal carcinoma in Hong Kong has decreased steadily since 1980, and a similar downward trend in incidence has been observed in Singapore Chinese since 1993 (1Go, 8Go). To determine if similar trends are occurring in US Chinese, we used the Surveillance, Epidemiology, and End Results (SEER) public-use database, combined with US Census data, to evaluate time trends in the incidence rates of nasopharyngeal carcinoma among Chinese living in Los Angeles County and in the San Francisco-Oakland metropolitan area (California) from 1992 to 2002.


    MATERIALS AND METHODS
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 
The data used in this analysis were from the SEER Program database of the National Cancer Institute, which gathers information on cancer incidence and survival in the United States from 14 population-based registries and three supplemental registries covering approximately 26 percent of the US population. We used the SEER 13 registry database and restricted our analysis to the Los Angeles and San Francisco-Oakland areas of California because of their relatively large Chinese populations. We further limited the analysis to cases diagnosed from 1992 to 2002, because data from Los Angeles are available only from 1992 and onward. The SEER statistical program (SEER*Stat version 6.1.4; National Cancer Institute, Bethesda, Maryland) was used to obtain the numbers and age distribution of the cases identified in these registries. A total of 519 Chinese residents of these areas with a microscopically confirmed diagnosis of nasopharyngeal carcinoma (those who had International Classification of Diseases for Oncology, Third Edition, site codes C110–C113 and C118–C119 and histology codes 8000–8481 and 8940–8941), excluding sarcoma, lymphoma, germ cell tumor, and melanoma cases, were identified.

We used the 1990 and 2000 US Census data to estimate the size of the Chinese populations in these two areas for each year during 1992–2002. In the 2000 US Census, respondents had the option of reporting being of more than one race for the first time. To take this into account, we estimated the denominator twice, first on the basis of persons who responded in 2000 that they were only Chinese, and then based on those who reported either being only Chinese or being a combination of Chinese and any other race. Using the second denominator, incidence rates were about 8 percent lower than when using the first denominator, but the incidence trends were identical. Thus, results are provided using only the first approach, that is, including in the denominator just those persons who designated themselves as being Chinese and no other race since, in the SEER data, only a single race is listed.

While data on the total number of Chinese living in Los Angeles and San Francisco-Oakland are available from both the 1990 and 2000 US Census, data on the age distribution of this population are available only from the 2000 US Census. To estimate the age distribution of the Chinese population in 1990, we assumed that the age distribution of the Chinese population in 1990 was the same as that of Asian-Pacific Islanders as a whole in 1990, since the age distribution of this group was available from the 1990 US Census. We grouped the population into 13 age categories (<30 years and ≥85 years as the youngest and oldest age groups, respectively, and divided the other age groups into 5-year intervals). The population in each age category for the years between 1990 and 2000 and the years 2001 and 2002 was estimated by linear interpolations and extrapolations, respectively. We used the 2000 US Chinese age-specific population distribution as the standard when calculating the age-adjusted incidence rates for each year. Using Stata, release 8.0 for Windows, statistical software (9Go), we performed negative binomial regression (10Go) with age adjustment to estimate linear trends in the incidence rates for this period expressed by proportional changes and associated 95 percent confidence intervals.


    RESULTS
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 
A total of 199 and 320 Chinese nasopharyngeal carcinoma cases diagnosed from 1992 to 2002 who met our eligibility criteria were identified from the Los Angeles and San Francisco-Oakland SEER registries, respectively. We pooled these two registries' data together to estimate trends in the incidence rates (table 1). There were 359 male cases and 160 female cases. The incidence rates for Chinese men were consistently higher than those for Chinese women. Incidence rates decreased by 37 percent (95 percent confidence interval (CI): –54, –12) in Chinese men during the 11-year period but only by 1 percent (95 percent CI: –40, 64) in Chinese women.


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TABLE 1. Age-adjusted incidence rates of nasopharyngeal carcinoma among Chinese in Los Angeles County and the San Francisco-Oakland metropolitan area of California, by year of diagnosis (1992–2002) and gender*

 
We examined the trends in the incidence of the separate histologic types of nasopharyngeal carcinoma among the male Chinese populations of Los Angeles and San Francisco-Oakland. Almost the entire decline in overall nasopharyngeal carcinoma incidence was due to a decline in the rate of type I tumors, which fell 71 percent (95 percent CI: –85, –45) (table 2). The incidence of type II tumors actually increased during this period, and the incidence of type III cases was relatively stable. However, the interpretation of trends for nasopharyngeal carcinoma histologic types is hindered by the high proportion (from one third to one quarter) of cases in which the specific type was not known.


View this table:
[in this window]
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TABLE 2. Age-adjusted incidence rates of nasopharyngeal carcinoma among Chinese men in Los Angeles County and the San Francisco-Oakland metropolitan area of California, by year of diagnosis (1992–2002) and histologic type*

 

    DISCUSSION
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 
The principal limitation of these analyses concerns the imprecision of our estimate of the size of the Chinese populations of Los Angeles and San Francisco-Oakland and the possible incomparability of the numerators and denominators from which incidence rates were calculated. However, any bias is likely to have been present to a similar degree throughout the 11-year interval of study, so our examination of time trends in nasopharyngeal carcinoma incidence is likely to be valid. Another limitation is that SEER race data are derived from medical record reviews, while census race data are based on self-report. The inconsistency in the way in which race information is collected and the potential for inaccuracy could lead to misclassification of some of the cases. This bias is also likely to have a similar degree of influence throughout the period.

During the last two decades of the 20th century, nasopharyngeal carcinoma incidence fell in Chinese men and women residing in Asia. In Hong Kong, the age-standardized incidence rate decreased from 28.5 to 20.2 per 100,000 person-years between 1980–1984 and 1995–1999 among Chinese men and from 11.2 to 7.8 per 100,000 person-years among Chinese women in the corresponding time periods (8Go). In Shanghai, the trends were similar. Incidence rates decreased from 5.6 per 100,000 person-years in 1973–1977 to 4.5 per 100,000 person-years in 1988–1992 for men and from 2.5 per 100,000 person-years to 1.8 per 100,000 person-years for women (1Go). While the incidence rates of nasopharyngeal carcinoma were relatively stable among Singapore Chinese of both sexes over the 20-year period between 1973 and 1992, there were an approximately 15 percent drop in incidence in men and a 30 percent drop in incidence in women during 1993–1997 (1Go). The incidence of nasopharyngeal carcinoma is increased in persons with a high level of consumption of preserved salted fish (11Go–13Go). Thus, one possible reason for the decline in nasopharyngeal carcinoma incidence among Chinese residents of Asia is a decline in the intake of preserved salted fish in this part of the world. Previous studies found that the incidence of nasopharyngeal carcinoma in southern China, as well as in other areas, displays an inverse relation with socioeconomic class (14Go, 15Go), and Cantonese-style salted fish is traditionally one of the cheapest foods available to supplement rice in southern China.

A previous SEER study reported that, in the US population as a whole, incidence rates of nasopharyngeal carcinoma were quite stable from 1974 to 1999 (16Go). Our results suggest that, among Chinese residents of California, nasopharyngeal carcinoma incidence has declined among men. The incidence rate of nasopharyngeal carcinoma in the US population during 1974–1999 was around 0.6 per 100,000 person-years (16Go), which is much less than the incidence rates in the Chinese population in this study. The incidence rates ranged from 8.40 to 15.18 per 100,000 person-years and from 2.72 to 6.92 per 100,000 person-years for Chinese men and women, respectively. Because we have no information about changes in dietary patterns or other potential nasopharyngeal carcinoma risk factors in Chinese residents of California during the latter part of the 20th century, we can only speculate on the basis for the observed trends. One possible explanation is recent changes in smoking patterns. A number of epidemiologic studies have reported that heavy smokers have an increased risk of nasopharyngeal carcinoma of from 1.7- to 6.4-fold compared with never smokers (17Go–20Go). In the United States, the prevalence of smoking has declined 24 percent among men between 1965 and 1993 but only 11 percent among women over this same period (21Go). We did not have information about changes in Chinese-Americans' cigarette smoking prevalence and intensity over the course of our study. If we assume that these followed a pattern similar to that of the whole US population, then changes in smoking patterns may to some extent account for the trends we observed. Further supporting this point is our observation that the decline in nasopharyngeal carcinoma incidence rates is limited to type I tumors, the only form of nasopharyngeal carcinoma that is related to cigarette smoking (17Go). Type I nasopharyngeal carcinoma is relatively uncommon among Chinese in Asia, so if the trends observed in our study continue, the distribution of histologic types of nasopharyngeal carcinoma in Chinese Americans may become more similar to that of Chinese in Asia.


    ACKNOWLEDGMENTS
 
This study was supported by Cancer Epidemiology Biostatistics Training Grant 5 T32 CA09168-29 from the National Institutes of Health and by grant N01-CN05230 from the National Cancer Institute.

The authors thank Dr. Lynda Voigt for help with access to the SEER data and Dr. Mei-Tzu C. Tang and Chloe Chien for biostatistical consultation.

Conflict of interest: none declared.


    References
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 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 

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