A hospital-based case-control study of ovarian cancer was conducted in London and Oxford between October 1978 and February 1983. Menstrual characteristics, reproductive and contraceptive history and history of exposure to various environmental factors were compared between 235 women with histologically diagnosed epithelial ovarian cancer and 451 controls. High gravidity, hysterectomy, female sterilisation and oral contraceptive use were associated with a reduced risk of ovarian cancer. Infertility and late age at menopause were associated with an increase in risk. While these factors were related, they were each found to be independently associated with ovarian cancer risk after adjusting for the effect of the other factors.
PIP: A case-control study of factors affecting risk of ovarian cancer, such as menstrual, reproductive, contraceptive and environmental exposure history, was based on women ascertained in London hospitals. 235 women with epithelial ovarian cancer, diagnosed at age 65 were included, of which 43% were serous, 15% were mucinous, 22% were endometrioid and 5% were clear cell tumors. The controls were not matched except by age distribution, since 63 of the cases were from a hospital treating only cancer patients. Multiple logistic regression techniques were used to compute maximum likelihood relative risk estimates. Nulligravidae had a 1.7-fold risk. Risk decreased with number of pregnancies. Those 1st pregnant after age 35 had significantly higher risk of ovarian cancer. Risk increased with duration of unprotected intercourse (p0.01), especially in nulligravidae, who had 2-fold the risk of other sexually active women. Use of oral contraceptives or sterilization significantly reduced risk of ovarian cancer, while use of no method elevated the risk. Risks decreased slightly with duration or use or orals. Risks increased with later age of natural menopause; women with hysterectomy had a much lower risk. A distinct trend toward increased risk with longer duration of ovulation was apparent (p0.001). Risks increased with length of breast-feeding. An 11-fold risk was computed for hysterectomized women who had used hormone replacement. Smoking was not a risk factor, but use of talc in the genital area was. These results corroborated other reports suggesting protection against ovarian cancer by use of oral contraceptives, increasing with duration of use, and persisting after ceasing pills.