The epidemiology of ovarian cancer: A population-based study in Olmsted County, Minnesota, 1935-1991

PURPOSE: To determine trends in incidence and survival between 1935 and 1991 and to evaluate risk factors for ovarian cancer among Olmsted County, Minnesota women. METHODS: All newly diagnosed cases of ovarian cancer among Olmsted County women in 1915-1991 were identified using the medical records linkage system of the Rochester Epidemiology Project. In order to assess trends, incidence rates in the subset of Rochester women were compared with Rochester rates for 1935-1974. Survival was evaluated by the Kaplan-Meier product-limit method. A case control analysis of risk factors compared Olmsted County women with invasive epithelial ovarian cancer and an age-matched group of women from the community by logistic regression. RESULTS: Altogether, 129 Olmsted County women were newly diagnosed with ovarian cancer in 1975-1991. The age-adjusted (to 1970 United States whites) incidence rate was 22.5 per 100,000 person-years. Median survival from initial diagnosis was 3.1 years. Compared to an equal number of controls, the 103 women with invasive epithelial disease were more likely to be nulliparous (odds ratio [OR] 1.9; 95% CI 0.95-3.9) bur less likely to have a history of thyroid disease (OR 0.4; 95% CI 0.2-0.8), hypertension (OR 0.4; 95% CI 0.1-0.9) or nonsteroidal estrogen use (OR 0.5; 95% CI 0.2-0.9). Prior hysterectomy (OR 0.5; 95% CI 0.2-0.9) and unilateral oophorectomy (OR 0.2; 95% CI 0.04-0.1) were also associated with reduced risk. CONCLUSION: The incidence of ovarian cancer in this community in 1975-1991 was little changed from rates 20 years earlier. There has been some improvement in survival from ovarian cancer in this population compared to 1935-1974, but still less than 50% survive for 5 years. Prior hysterectomy and unilateral oophorectomy appear protective for ovarian cancer. Ann Epidemiol 2000;10:14-23. (C) 2000 Elsevier Science Inc. All rights reserved.