Bladder cancer: epidemiology and risk factors in Bulawayo, Zimbabwe

The incidence of bladder cancer, and the importance of some selected risk factors in its etiology, were estimated from the data collected in the cancer registry of Bulawayo, Zimbabwe, during the period 1963-77. Cancer cases were interviewed with a standard questionnaire, and more than 70 percent of these were complete. Incidence rates in the urban population of Bulawayo in the first 10-year period were relatively high, with age standardized rates of 17.9 per 100,000 in men and 9.5 in women. Risk-factor distribution was compared in 680 bladder cancer cases (494 males, 186 females) and a control group comprising other cases with non-tobacco-related cancers (8,201). Seventy-one percent of bladder cancer cases were squamous cell carcinomas. The presence of schistosomiasis, evaluated from past history of bilharzia or hematuria, was associated with a significantly increased risk of bladder cancer in both genders (odds ratio [OR] = 3.9 for men, 5.7 for women), a result reflected in the differing risk by province of residence, which correlated with the prevalence of infection among cancer cases. The proportion of bladder cancer attributable to schistosomiasis was estimated to be 28 percent. Social status, as reflected by education level, also influenced risk (ORs for literate cf illiterate males = 0.6), but tobacco smoking in men had no effect on the risk of squamous cell tumors. For transitional cell carcinomas or adenocarcinomas, there was a nonsignificant increased risk of 2.0 in the highest smoking categories (15 g of tobacco per day), compared with non smokers.