Epidemiology of hairy cell leukemia in Los Angeles County

The descriptive epidemiological characteristics of hairy cell leukemia (HCL), a rare chronic lymphoproliferative disorder, were examined by using incidence data collected from 1972 to 1987 by the Cancer Surveillance Program, the population-based cancer registry for Los Angeles County. During the study period, 208 incident cases of histologically confirmed HCL were diagnosed. HCL comprised 2% of all leukemias diagnosed in Los Angeles County during the study period. HCL risk was concentrated in white males; there were few black and Asian patients for analysis. Overall, the age-adjusted incidence rate of HCL for men (2.9/million population) was 4.8 times greater than that for women (0.6/million population). Using data from all cancer patients diagnosed during the study period, Jewish men had significantly greater risk of HCL than Protestant men (odds ratio (OR) = 3.0, P less than 0.0001); there was no significant variation in risk of HCL by religion for women. For men, the OR was significantly elevated for professional and technical workers (OR = 2.1, P = 0.001); within this category of occupations, risk was significantly elevated for engineers (OR = 3.3, P less than 0.0001) and university faculty and school teachers (OR = 4.0, P = 0.0008). HCL patients were more than twice as likely to have multiple primary cancer diagnoses as other cancer patients. Since the majority of the other primary cancer diagnoses occurred prior to (greater than 1 year) or concurrent with (less than or equal to 1 year) the HCL diagnosis, this greater frequency of multiple primaries in HCL patients may be due to impaired immune function.