The protective effects of combined oral contraceptives against endometrial cancer appeared to be restricted to women who had used them for 1 year or longer and was concentrated in nulliparous women. There was no evidence that long-term oral contraceptive use of more than 10 years or oral contraceptive use that began 16 or more years ago, shortly after oral contraceptives were introduced in this country, increased the risk of breast cancer. Furthermore, there was no indication of any increased risk of breast cancer due to oral contraceptive use for high-risk women such as those with family histories of breast cancer or with previous biopsies for benign breast disease. Similarly, there was no evidence of an increased risk of breast cancer for women who used oral contraceptives before their first pregnancy. It is specifically designed to clarify the association between oral contraceptive use and breast, endometrial, and ovarian cancer.
Methodologic biases are unlikely to account for the study's findings.
Selection bias was minimized by attempting to enroll all women from the eight geographic areas who have newly diagnosed breast, endometrial, or ovarian cancer and by selecting controls at random from the same areas. Because of the widespread use of oral contraceptives and the common occurrence of endometrial and ovarian cancer, the protective effects of oral contraceptives against these tumors could have a large public health impact. The reduced risk of cancer among women who have used oral contraceptives would result in the prevention of over 1,700 cases of ovarian cancer and over 2,000 cases of endometrial cancer in the United States each year. Agreement between women's histories of oral contraceptive use and physician records. This conversion may have resulted in character translation or format errors in the HTML version.