Objectives Uterine carcinosarcoma (UC) is rare and carries a poor prognosis. It represents only 1–2% of uterine cancers and less than 5% of all uterine malignancies. Although these tumors usually arise de novo, some cases developed under Tamoxifen therapy have been reported. We aim to report our institution’s experience.

Methods A retrospective study of 11 women with endometrial carcinosarcoma after breast cancer were treated at Salah Azaiez Institute of Oncology from 2004 to 2014.

Results The mean age of UC diagnosis was 64 years (50–82 years). All patients were given adjuvant hormone therapy by Tamoxifen for breast cancer. The mean duration of Tamoxifen use was 42 months (3–60 months) with a mean cumulative dose of 25709mg (1800–36500mg). The main presenting symptom of UC was post-menopausal bleeding. Ultrasound showed thickened endometrium in four cases. Endometrial biopsy revealed UC in three cases. Surgery was performed in ten cases. It consisted of total hysterectomy and bilateral oophorectomy in all cases; we performed lymphadenectomy in three cases. Adjuvant chemotherapy and radiotherapy were performed in three cases. The median follow-up after surgery was nine months (1–64 months). One patient developed a peritoneal recurrence five months after surgery. Three women developed bone metastasis from their uterine cancer, and two patients developed liver metastases from their breast cancer.

Conclusions The survival benefits associated with five-year adjuvant Tamoxifen counterbalances the low morbidity and mortality risk associated with endometrial adenocarcinoma development. Things are different with UC and its pejorative prognosis. The rarity of this tumor makes the risk of its development undetermined.