Case-control studies of prostate cancer in blacks and whites in southern California.

To identify risk factors for prostate cancer and to try to explain the high risk of blacks relative to whites, case-control interview studies of prostate cancer were conducted in both populations in southern California. Both studies included 142 pairs of cases and population controls matched on age. Cases in blacks were identified by the population-based tumor registry of Los Angeles County and cases in whites were identified by a population-based tumor registry of a southern California retirement community. A past history of venereal disease was associated with a high risk of prostate cancer in both populations [relative risk (RR) = 2.3 in whites; RR = 1.7 in blacks]. The result in blacks was statistically significant (P = .03). Black cases tended to have more frequent sexual intercourse than black controls at all ages; the difference became statistically significant for intercourse late in life. Data from controls suggested that, overall, blacks have earlier and more frequent sexual activity than whites, but the two populations were dissimilar in social class characteristics. Fat intake was a risk factor for prostate cancer in both populations, but vitamin A consumption and protein intake were inconsistently related or unrelated to prostate cancer risk. While beta-carotene was not consistently related to risk, there was some indication that in persons with low fat intake, low beta-carotene intake may be associated with high risk. Circumcision was negatively associated with risk in both populations (RR = 0.5 in whites; RR = 0.6 in blacks). These results are discussed in the context of major etiologic hypotheses for prostate cancer.