Oral Contraceptives as Related to Cancer and Benign Lesions of the Breast 2
Authors: Elfriede Fasal, Ralph S. Paffenbarger
Journal: JNCI Journal of the National Cancer Institute (1975)

We conducted a case-control study to search for any relationship between use of oral contraceptives and development of breast cancer or benign breast disease. Women less than 50 years old with these diseases were matched with 2 controls by age, race, religion, and hospital. Home interviews elicited information on oral contraceptive use and other host and environmental factors. The study population comprised 1,770 women, including 452 with breast cancer and 446 with benign breast disease. The relative risk of developing cancer or benign disease was measured by matched set and summary chi-square analyses. Although the relative risk of developing breast cancer among "ever-users" of oral contraceptives was 1.1, the risk among women using oral contraceptives for 2-4 years was 1.9 (significantly increased). This risk estimate reached 2.5 for the 2- to 4-year users if they were still taking oral contraceptives when entered into study. Moreover, prior biopsy for benign breast disease increased the cancer risk among long-term users by as much as 11-fold. The relative risk of breast cancer did not vary by age, interval since first use, earliest year of use, or interval since last use. These results could be interpreted to indicate that oral contraceptives did not induce breast cancer but may have accelerated the growth rate of preexisting breast cancer. The relative risk of developing benign breast disease among ever-users of oral contraceptives was 0.8 (significantly reduced); it decreased with longer duration of use until it reached 0.2 for women who took these hormones 8 years or more. The relative risk of benign breast was not affected by earliest year of use or interval since last use. We concluded that oral contraceptives reduced the incidence of benign breast disease, but that use of steroid hormones is ill-advised for women with already established benign breast disease.A 3-year case-control study of 1770 women under age 49 from the San Francisco Bay area, who were admitted to area hospitals with newly diagnosed breast cancer or with benign noninflammatory breast lesions, is reported. There were 452 with breast cancer, 446 with benign breast disease, 433 with other medical conditions, and 439 with other surgical conditions. Detailed information was obtained concerning each subject's contraceptive practices, menstrual and obstetric experiences, hormone use, medical and surgical history, and family history of breast cancer. Those without breast disease were selected as suitable controls concerning risk factors. In all instances the risk of breast disease was compared between women who had or were using oral contraceptives and others. Current users of oral contraceptives were 16% of patients with breast cancer and 13% of control patients. Contraceptive users were 9% of patients with benign breast disease. 1/2 of those using oral contraceptives had done so for 2 years or less. Only 15% of those who used these drugs had done so for over 6 years. Relative risk for all age groups of developing breast cancer was estimated to be increased by 10% among oral contraceptive users. The risk was less in older patients. With duration of oral contraceptive use, risk was significant only for the 2-4 year users in whom it was increased twofold (p less than .01). Relative risks were the same with the different dose levels of contraceptive compounds. Among ever-users, cancer risk was much greater (six to elevenfold) for women with prior history of biopsy for benign breast disease, particularly among those who had used oral contraceptives more than 6 years. Other contraceptive measures are recommended for such women. Observation for long-term effects should include study of type-specific benign disease as related to use of the hormones and later development of cancer. It may be that use of oral contraceptives accelerated the growth rate of preexisting subclinical malignant lesions and that after 2 years these lesions reach the level of clinical recognition, all being diagnosed within the next 2 years.