Soft tissue sarcoma unmasked: An atypical presentation of primary cutaneous B-cell lymphoma

Introduction: Primary cutaneous follicle center lymphoma (PCFCL) is the most common subtype of primary cutaneous B-cell lymphoma and is typically an indolent malignancy with an excellent prognosis. However, atypical presentations may mimic soft tissue sarcoma or high-grade lymphoma, creating significant diagnostic challenges. Case Report: In this report, we describe a unique case of a young male with a history of systemic lupus erythematosus (SLE) who presented with a slowly enlarging, ulcerated soft-tissue mass of the lower back with associated drainage, pain, fever, and weight prompting treatment with dose-adjusted R-EPOCH (etoposide, prednisone, vincristine, cyclophosphamide, doxorubicin, and rituximab) loss. Upon admission, cross-sectional imaging and fluorine-18 fluorodeoxyglucose (18F-FDG) positron emission tomography–computed tomography (PET-CT) revealed a large (15 cm) right dorsal soft tissue mass with intense FDG uptake. Core needle biopsy initially demonstrated a high-grade appearing B-cell lymphoma with a concern for high grade lymphoma. Following additional immunostaining and multidisciplinary hematopathology review, the diagnosis was revised to PCFCL with a diffuse growth pattern. The patient completed four cycles of inpatient chemotherapy with a reduction in mass size after each cycle. Conclusion: Here we present a case of PCFCL with a diffuse growth pattern that mimicked both soft-tissue sarcoma and high-grade B-cell lymphoma, highlighting the importance of prompt tissue diagnosis and comprehensive pathologic evaluation.