NASOPHARYNGEAL CANCER IN A LOW-RISK POPULATION - DEFINING RISK-FACTORS BY HISTOLOGICAL TYPE

Nasopharyngeal cancer (NPC) is a major public health problem in parts of Southeast Asia and North Africa, but is rare among whites and black s, Although infection with the EBV and genetic susceptibility appear t o play large roles in high-incidence populations, migrant studies sugg est that environmental factors may also be important. Aside from the h igh risks associated with ingestion of salted fish, surprisingly few o ther risk factors have been established from studies in endemic areas, We studied a low-incidence population to determine whether tobacco us e, alcohol consumption, and certain medical conditions and treatments are related to NPC and to examine variations in risk by histology, We reasoned that new relationships might he best identified in the absenc e of strong causal pathways, such as intake of preserved foods and gen etic susceptibility, A population-based case-control study was conduct ed from 1987 to 1993 at five cancer registries in the United States: w estern Washington, metropolitan Detroit, Connecticut, Iowa, and Utah, Controls were identified by random digit dialing and frequency matched to the gender and age distribution of cases at each registry, Telepho ne interviews were completed by 231 cases and 246 controls, We observe d a strong dose-response relationship between cigarette smoking and ri sk of differentiated squamous cell carcinoma (test for trend, P <.001) , The highest risk [odds ratio (OR), 6.5; 95% confidence interval (CI) , 2.0-21.3] occurred among current smokers with a history of more than 60 park-years, In contrast, there was no evidence that undifferentiat ed or nonkeratinizing carcinomas were associated with cigarette smokin g, Similarly, a significant increase in risk was observed for the heav iest alcohol consumers (21 or more drinks/week) only for differentiate d squamous cell carcinomas (OR, 2.9; 95% CI, 1.2-6.9), The association s with cigarettes and alcohol appeared to be stronger among persons 50 years or older, There was a suggestion that diagnosis with infectious mononucleosis (a marker of late infection with EBV) is linked with de creased NPC risk (OR, 0.4; 95% CI, 0.1-1.1), This report indicates tha t over two-thirds of differentiated squamous cell NPC cases arising in older persons in the United States can be accounted for by cigarettes and alcohol, but leaves unexplained cases arising in the young and ca rcinomas of undifferentiated or nonkeratinizing histology, Future stud ies of NPC need to take into account histology and age in evaluating t hese and other environmental and genetic risk factors.