Primary Extranodal Non-Hodgkin Lymphoma-A Rare Presentation as a Soft Tissue Mass

Non-Hodgkin lymphoma (NHL) is an adverse group of neoplasms that can occur at nodal and extranodal sites with varied prognosis. NHL involving soft tissue as a primary site accounts to 0.1% of cases and may mimic sarcoma; therefore, it is necessary to differentiate them as described by travis and co-authors, similarly. We describe a case of 72-year-old male patient with a mass in the right thigh. Magnetic resonance image reported a benign soft tissue tumour; fine-needle aspiration cytology suggested a soft tissue sarcoma and computed tomography imaging reported no other sites of involvement. PET (Positron emission tomography) scan done after first cycle of chemotherapy revealed enlarged right-side femoral and external iliac group of lymph nodes. On histological examination and immunohistochemistry, it was diagnosed as primary diffuse large B-cell lymphoma involving skeletal muscle. The case is presented to highlight the diagnostic difficulties due to its presentation on a rare site.