Ovarian cancer. Incidence and case‐control study

Records of all Rochester Minnesota residents with a diganosis of ovarian cancer from 1935 through 1974 were reviewed. These included records at the Mayo Clinic and at other medical facilities serving the local population. For the incidence study a total of 151 cases met the residential diagnostic and pathologic criteria. Risk factors for epithelial ovarian cancer occurring in Rochester from 1945 to 1974 were examined in 116 patients and 464 controls. The relative risks of ovarian cancer associated with various risk factors were estimated by the matched quintuplets method of Miettinen when the value of the factor was known for all patients and controls. Among the 116 patients with epithelial ovarian cancer and 464 controls nulliparity was the only significant risk factors - relative risk 1.8. Other suspected risk factors - hypertension obesity age at menopause prior therapeutic pelvic radiation and prior exogenous estrogen - did not differ significantly between patients and controls. The ovarian cancer patients were found to have a significantly lower frequency of prior hysterectomy and of unilateral oophorectomy than the control group. The data reveal that hysterectomy even when one or both ovaries are preserved is associated with a lower risk of subsequent ovarian cancer. The incidence rates of ovarian cancer in Rochester were found to be higher than those reported from Connecticut and from other parts of the world with high rates of ovarian cancer. For the last three decades there has been a slight decline in the incidence of ovarian cancer in Rochester. Both of these pheonomena may be due to the high proportion of Rochester women particularly in the earlier decades of the study who were nulliparous.