When the endometrioid adenocarcinoma and the endometrial stromal sarcoma meet: A report of an extremely rare case.

Introduction: Collision tumors are characterized by the coexistence of two adjacent, but histologically distinct tumors. This entity can occur between tumors originating from the same organ or between metastases from other sites. Case presentation: A 49-year-old postmenopausal female with abnormal vaginal bleeding and abdominal pain was diagnosed with two coexistent tumors, a grade 1 endometrioid carcinoma and a pT2 undifferentiated stromal sarcoma (USS). On the first time, the patient underwent a total abdominal hysterectomy with bilateral salpingo-oopherectomy and one month later, she was diagnosed with recurrence. Then, a second surgical excision of the recurrent tumor was performed including exploratory laparotomy and anterior pelvic exenteration. She had an uneventful postoperative period, but unfortunately a month following the second operation she passed away. Conclusion: We aim to raise awareness of these rare synchronous malignancies and highlight the importance of having a broad differential diagnosis in a patient presenting with abnormal vaginal bleeding. Further studies with larger patient populations are needed to shed light in etiology and pathogenesis of the concurrence of two malignancies with different embryological origin in the same organ, in order to optimize management of these patients.