Characteristics relating to ovarian cancer risk: collaborative analysis of seven U.S. case-control studies. Epithelial ovarian cancer in black women. Collaborative Ovarian Cancer Group.

BACKGROUND: Previous epidemiologic studies of ovarian cancer have focused chiefly on White women, who have a higher incidence of ovarian cancer than Black women. No study has previously examined risk factors for ovarian cancer among Black women.

PURPOSE: This study was designed to evaluate the risk of epithelial ovarian cancer in Black women in relation to reproductive characteristics such as pregnancy, oral contraceptive use, and breast-feeding, and to determine whether differences in reproductive factors between Black and White women account for differences in ovarian cancer incidence.

METHODS: Combining interview data from seven case-control studies, we compared reproductive characteristics of 110 Black case subjects with a diagnosis of epithelial ovarian cancer between 1971 and 1986 with characteristics of 251 Black population control subjects and 114 Black hospital control subjects. We also compared the prevalence of reproductive factors in 246 Black population control subjects and 4378 White population control subjects and estimated the fraction of Black-White differences in ovarian cancer incidence attributable to racial differences in prevalence of these characteristics.

RESULTS: Decreased risks of epithelial ovarian cancer in Black women were associated with parity of four or higher (odds ratio [OR] = 0.53; 95% confidence interval [CI] = 0.25-1.1), breast-feeding for 6 months or longer (OR = 0.85; 95% CI = 0.36-2.0), and use of oral contraceptives for 6 years or longer (OR = 0.62; 95% CI = 0.24-1.6). A greater proportion of Black women (48%) than White women (27%) reported four or more term pregnancies, and Black women (62%) were more likely than White women (53%) to have breast-fed their children. Oral contraceptive use was more common among White women (59%) than Black women (51%).

CONCLUSION: Differences in the prevalence of other factors related to ovarian cancer risk or differences in genetic susceptibility must explain most of the Black-White differences in incidence of ovarian cancer.