Reproductive factors of ovarian and endometrial cancer risk in a high fertility population in Mexico.

A case-control study was carried out in Mexico City during 1995-1997 among women with epithelial ovarian cancer (84 cases) and endometrial cancer (85 cases). The control group consisted of 668 healthy women, matched according to age categories. In a multivariate analysis, the reproductive risk factors for ovarian and endometrial cancer are similar. The risk of ovarian cancer was inversely related to the number of full-term pregnancies; the odds ratio (OR) was 0.17 and the 95% confidence interval (CI) was 0.05-0.54 when comparing nulliparous women versus those with more than seven pregnancies. For endometrial cancer, a similar association was observed (OR, 0.11; 95% CI, 0.04-0.34). The use of oral contraceptive hormones was inversely associated with both ovarian (OR, 0.36; 95% CI, 0.15-0.83) and endometrial cancer risk (OR, 0.36; 95% CI, 0.14-0.90). In women with a history of more than 8.7 years without ovulation, the risk of ovarian cancer decreased four times (OR, 0.23; 95% CI, 0.10-0.50), and that of endometrial cancer decreased more than five times (OR, 0.17; 95% CI, 0.08-0.35). These two neoplasms are clearly typified as hormone dependent, and it is possible to establish that "ovulation" and "exfoliative" mechanisms jointly determine the level of risk for both ovarian and endometrial cancer.