A Rare Monophasic Synovial Sarcoma of the Inguinal Region Mimicking Lymphadenopathy: A Case Report

Introduction Synovial sarcoma is a rare and highly aggressive type of soft-tissue sarcomas, accounting for 5-10% of all sarcomas [1]. This malignancy predominantly affects young adults aged 15 – 40 and has a 5-year survival rate of 60-80% in the absence of metastases[1,2]. The symptoms are usually non-specific and can overlap with benign conditions, leading to a risk of misdiagnosis and missed malignancy [1,3]. Case Presentation A 21-year-old female presented to the family medicine physician with complaints of a lump in the left groin area, painful when pressed. Enlarged lymph nodes were noticed 6 weeks ago with no size reduction since. Ultrasound showed a 5 x 2 cm enlarged lymph node. Surgical excision of the lymph node was performed, and a biopsy was taken. Pathological examination revealed no recognizable features of a lymph node. Instead, a cellular tumor was found with oval cells, dispersed chromatin nuclei, eosinophilic cytoplasm. 8 mitoses per 10 HPF, no necrosis. Immunostaining showed positivity with TLE-1, EMA, CD99, and synaptophysin, while beta-catenin, S100, WT1, NSE, actin, desmin, pan-cytokeratin, CD177 and CD34 were negative. The Ki67 proliferation index was about 20%. Conclusion: the findings indicate a malignant soft tissue tumor with features consistent with monophasic synovial sarcoma G2. Molecular testing confirmed SS18 (18q11.12) gene rearrangement in 96% of interphase nuclei. Discussion In this clinical case, a translocation involving the SS18 gene was identified, which is strongly associated with the development of synovial sarcoma and poor prognosis [1,3]. The neoplasm typically originates in the soft tissues near the extremities and joints [2]. Occasionally it can develop in the groin area, but this is an extremely rare finding with a limited number of cases reported in the literature [4,5]. Conclusions Monophasic synovial sarcoma of the inguinal region is an atypical and rare site of sarcoma development. This case highlights the importance of considering sarcoma in the differential diagnosis of persistent inguinal masses that mimic lymphadenopathy, emphasizing the need for early recognition, accurate histopathological assessment, and molecular testing to avoid misdiagnosis and ensure timely management.