Of eight young women, seven had a diagnosis of well-differentiated endometrial adenocarcinoma and one had atypical endometrial hyperplasia. The average age was 40.1 years, with 6.04 years of dimethisterone-ethinyl estradiol (Oracon) sequential contraceptive use.
The patients were not typical of those in whom endometrial carcinoma develops. Although these cases do not prove that long-term administration of dimethisterone-ethinyl estradiol causes endometrial adenocarcinoma or atypia, they indicate that it may do so.
(JAMA 236:923-926, 1976)
Kaufman RH, Reeves KO, Dougherty CM. Severe Atypical Endometrial Changes and Sequential Contraceptive Use. JAMA. 1976;236(8):923–926. doi:10.1001/jama.1976.03270090017018