Risk of Ovarian Cancer Is Lessened by Childbearing, Pill Use and Hysterectomy

Abstract

In Ontario Canada data on reproductive history were obtained by interviews with 450 of 631 patients aged 35-79 diagnosed with primary malignant or borderline malignant epithelial ovarian tumors between November 1989 and October 1992. These data were compared with 564 age and residence-matched controls. Logistic regression analysis revealed that 1) 77% of cancer patients had given birth vs. 89% of controls; 2) that parous patients had 2.5 term pregnancies vs. 2.8 among controls; 3) that patients who ever-used oral contraceptives (OCs) used them for 4.2 vs. 5.5 years; 4) that women who had given birth were 60% less likely to develop ovarian cancer; 5) that the odds ratio decreased from 0.64 among those who had one full-term pregnancy to 0.23 among those who had 5 or more; 6) that the risk of ovarian cancer decreased 22% for each term pregnancy and that this decrease increased slightly for women with hysterectomy or a history of periods of infertility; 7) that breast feeding appeared to reduce risk; 8) that ever-users of OCs had only 50% the risk of never-users with those who used OCs for 10 or more years having a third of the risk; 9) that each successive year of OC use reduced risk by 8% among all women and among parous women and by 13% among nulliparous women; 10) that sterilization caused a small decrease in risk; 11) that hysterectomy reduced risk by about 50% and the length of time since hysterectomy did not alter this effect; and 12) that infertility is not an important factor in ovarian cancer risk. These findings confirm those reported from other studies that parity OC use and hysterectomy reduce overall ovarian cancer risk.