Abstract
INTRODUCTION AND IMPORTANCE: Diffuse large B-cell lymphoma (DLBCL) is the most common type of non-Hodgkin's lymphoma (NHL), known for its aggressive nature and tendency for extranodal extension. Extranodal involvement occurs in up to 40 % of cases, with primary lymphoma in soft tissue, particularly skeletal muscle, being exceedingly rare. This report presents a rare case of primary extranodal DLBCL in the calf muscle. CASE PRESENTATION: A 35-year-old man presented with an ulceroproliferative growth in left calf muscle, initially diagnosed as squamous cell carcinoma (SCC). Imaging studies, including CECT and MRI, were inconclusive, prompting a histological examination. Biopsy revealed large malignant cells with high mitotic activity, positive for LCA, CD20, BCL-2, MUM1, and CD10, confirming a diagnosis of primary extranodal DLBCL. The patient underwent resection followed by six cycles of chemotherapy (R-CHOP) and field radiation therapy. A follow-up PET showed significant improvement, with no evidence of disease recurrence. CLINICAL DISCUSSION: DLBCL often presents with rapidly growing tumors in lymph nodes or extranodal sites. Primary skeletal muscle lymphoma, particularly of the DLBCL subtype, is extremely rare, constituting about 0.5 % of extranodal lymphomas. Diagnosis typically involves imaging and biopsy, with immunohistochemistry (IHC) being crucial for accurate classification and treatment planning. CONCLUSION: DLBCL, while common among NHLs, rarely presents as primary extranodal lymphoma in skeletal muscle. The presented case underscores the importance of considering DLBCL in differential diagnoses for atypical soft tissue masses and the effectiveness of R-CHOP chemotherapy in managing this rare presentation. Prompt and appropriate treatment, such as R-CHOP chemotherapy, is essential for favorable outcomes.