Malignant Vulvar Glomus Tumor Mimicking a Small Round Cell Sarcoma: A Diagnostic and Therapeutic Challenges

Abstract

Background: Malignant glomus tumors are rare neoplasms, and vulvar involvement is exceptionally uncommon, creating significant diagnostic challenges. Aims: This case study reports an exceptional case of malignant glomus tumor of the vulva presenting with small round cell morphology, and to discuss the diagnostic and therapeutic challenges of this rare entity. Presentation of Case: A 57-year-old postmenopausal woman presented with a progressively enlarging mass of the right mons pubis extending to the upper right labia majora. Initial histopathology on the excision specimen suggested a poorly differentiated granulosa cell tumour. Following local recurrence, a re-biopsy was performed and an extended immunohistochemical panel was applied: CD99 positivity, diffuse vimentin positivity, focal pan-cytokeratin expression, and low desmin expression were identified, while calretinin, inhibin, synaptophysin, chromogranin, CD56, and CD45 were negative. Molecular studies excluded EWSR1 and SS18 gene rearrangements and FOXL2 mutation. After expert multidisciplinary pathological review integrating morphology, immunoprofile, and molecular exclusion of differential diagnoses, the diagnosis of malignant glomus tumour was established. The patient received six cycles of doxorubicin and ifosfamide-based chemotherapy (MAI protocol, every 21 days), achieving marked radiologic regression including resolution of pulmonary micronodules. Surgical resection of the tumour bed showed no residual viable tumour. Discussion: Malignant glomus tumors are rare mesenchymal neoplasms representing fewer than 1% of soft tissue sarcomas. Vulvar localization is exceptionally uncommon and may pose significant diagnostic challenges, particularly when histology demonstrates small round cell morphology mimicking other high-grade sarcomas. Accurate diagnosis relies on integrated histopathological, immunohistochemical, and molecular evaluation. Conclusion: This case underscores the diagnostic complexity of extra-digital glomus tumors and highlights the importance of molecular testing and multidisciplinary management in rare vulvar mesenchymal neoplasms. Sarcoma-based chemotherapy may provide meaningful response in selected cases.