Beneath the Surface: Exploring the Complexities of Fibromyxoid Sarcoma

Abstract

Introduction: Low-grade fibromyxoid sarcoma (LGFMS), or Evans tumor, is a rare soft tissue sarcoma with fibrous and myxoid areas, whorled pattern, and low cellularity. It comprises <5% of cases, commonly affecting trunk and extremities, and rarely the retroperitoneum or mediastinum.

Aim & Objectives: To present a rare case of low-grade fibromyxoid sarcoma presenting as a pelvic mass mimicking a broad ligament fibroid and to highlight its diagnostic challenges and management.

Case Presentation: A 50-year-old female (P2L2) presented with 2 months of amenorrhea and a history of T2DM and hypertension. Examination revealed a normal-sized anteverted uterus with a hard, non-tender right forniceal mass. Ultrasonography suggested a 78 × 62 mm hypoechoic pelvic lesion, likely a broad ligament or exophytic fibroid. Intraoperatively, a retroperitoneal mass (8 × 4 cm) above the right internal iliac vessels was identified, excised, and sent for histopathological examination.

Results: Histopathological examination confirmed the diagnosis of low-grade fibromyxoid sarcoma. The tumor showed low to moderate cellularity with bland spindle-shaped (fusiform) cells arranged in a whorled pattern within a collagenized stroma, along with abrupt transition to myxoid areas. Immunohistochemistry typically shows MUC4 positivity, and cytogenetic analysis is associated with t(7;16) (q32–34; p11) translocation resulting in FUS–CREB3L2 fusion.

Conclusion: Low-grade fibromyxoid sarcoma is a rare soft tissue tumor that can mimic a fibroid when arising in the retroperitoneum, leading to diagnostic difficulty. Accurate diagnosis relies on histopathology and immunohistochemistry. Complete surgical excision with wide margins remains the mainstay of treatment, with or without adjuvant radiotherapy.