Failure of megestrol acetate to reverse tamoxifen induced endometrial neoplasia: two case reports

Tamoxifen's agonist effect on the endometrium has been associated with an increased incidence of endometrial carcinoma. It has been suggested that this agonist effect may be averted by the concomitant use of a progestational agent. We report two patients with breast cancer receiving tamoxifen who developed endometrial carcinoma and atypical endometrial hyperplasia, respectively. In one patient, this occurred despite the use of concomitant megestrol acetate. In the other patient, tamoxifen-associated endometrial hyperplasia persisted and progressed despite cessation of tamoxifen and initiation of megestrol acetate therapy. These cases may have implications for strategies to avert tamoxifen induced endometrial neoplasia.