Challenges in Distinguishing Rectal Leiomyosarcoma from Ovarian Malignancy: A Diagnostic Conundrum

Abstract

Introduction: Rectal leiomyosarcoma is a rare malignant mesenchymal tumor accounting for <0.1% of all malignant colorectal neoplasms and carries a grave prognosis. Case Presentation: A 50-year-old postmenopausal, P3L3 woman presented with complaints of abdominal pain for two months, dark-colored loose stools, 10-15 episodes per day for 2-3 months, and gradual weight loss for 4-5 months. On ultrasonography and MRI of the pelvis, a large irregular lobulated ill-defined solid lesion was seen arising from the right side of the pelvis measuring 14x8x14cm. The right ovary was not observed to be separate from the mass. There was omental thickening and peritoneal deposits with ascites. The final impression suggested a right-sided malignant ovarian mass with peritoneal dissemination (ORADS-5) with a differential leiomyosarcoma. Her tumor markers (CA- 125; CA19-9, and CEA) were raised. Given the strong dilemma between ovarian malignancy and leiomyosarcoma and the advanced stage of the disease, the patient was planned for an ultrasound-guided biopsy of the lesion. The histopathological report revealed atypical spindle cell proliferation with myoid features with the presence of multiple mitotic figures. The diagnosis of rectal leiomyosarcoma was further confirmed with immunohistochemical tests, which were positive for actin and desmin and negative for CD 117 and S100. The patient was referred to oncosurgeon for further management and was planned for surgical resection followed by chemotherapy with intravenous doxorubicin. Conclusion: Rectal leiomyosarcoma is commonly misdiagnosed as ovarian malignancy because of its exophytic growth and similar clinical features at the time of the presentation. Hence, clinicians must be aware of these differentials for the successful management of cases.