Background: Tamoxifen therapy is related to endometrial adenocarcinoma. Bicornuate uteri are more common than assumed. There are a few reports of endometrioid carcinoma arising in a bicornuate uterus, but none of these discuss a serous papillary component or an association with tamoxifen therapy.
Case: This is a case of a mixed endometrioid and serous papillary endometrial carcinoma arising in one horn of a bicornuate uterus. Multiple benign polyps were also present.
Conclusion: Adequate tissue sampling of both horns is critical to arriving at a timely and accurate diagnosis of malignancy in patients with a bicornuate uterus.