Cancer patterns and risk factors in the African population of southwestern Zimbabwe, 1963-1977.

The incidence of 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 1963-1977. Cancer cases were interviewed with a standard questionnaire, and more than 71% of these were complete. In men, the most frequent cancer sites were liver, esophagus, and lung, while in women, cervical cancer was the dominant malignant tumor, followed by cancers of the liver, breast, and bladder. Risk factors of cancer cases were estimated by case-control analysis in which other cancers (excluding tobacco-related cancers in men and hormone-related cancers in women) were considered as controls. In men, tobacco smoking was associated with increased risk of lung cancer (odds ratio OR2, 5.2) and esophagus cancer (OR, 5.6) in the highest consumption category (15 g of tobacco per day) compared to nonsmokers. Copper (OR, 1.5), gold (OR, 1.5), and nickel (OR, 2.6) miners had an increased risk of lung cancer, but no increase was found among asbestos miners (OR, 0.7). There was no independent effect of alcohol consumption on the risk of esophagus cancer. The presence of schistosomiasis was associated with a significantly increased risk of bladder cancer (OR, 3.9). The risk of invasive cervical cancer increased with number of children--the estimated odds ratio was 1.8 in women with six or more births--but no consistent association was found for first intercourse. In postmenopausal women, the risk of breast cancer increased with age at first pregnancy (but not in the highly fertile) and decreased with high parity, if age at first pregnancy was 19 or more.