Incidence of endometrial cancer in relation to the use of oral contraceptives.

Female residents of King and Ierce Counties in the state of Washington in whom endometrial cancer was diagnosed during 1975--77 were interviewed concerning prior use of oral contraceptives. Their responses were compared with those of a random sample of women from the same population. Women who had taken Oracon (0.1 mg of ethinyl estradiol and 25 mg of dimethisterone) were estimated to have a risk of endometrial cancer 7.3 times that of other women (P = 0.007). This elevation in risk was not seen in users of other sequential preparations. Women who had used combined oral contraceptives had only 50 per cent of the incidence of endometrial cancer of nonusers (P = 0.05), although the protective effect was not evident among those who subsequently took menopausal estrogens for more than two years. These associations suggest that development of neoplasia in the endometrium can be extremely sensitive to hormonal factors: if an oral contraceptive, like Oracon, emphasizes the estrogenic component, promotion of cancer can result; if like combined preparations, the contraceptive emphasizes the progestational component, protection against cancer can result.