ABCL-665 Diffuse Large B-Cell Lymphoma of the Bone Recurring in the Skin: A Case Report

Primary lymphoma of the bone (PLB) is a rare disorder, making up 5% of primary bone tumors and 5% to 7% of extranodal lymphomas. Diffuse large B-cell lymphoma (DLBCL) is the most common type, accounting for up to 90% of cases. PLB typically affects the axial skeleton more than the appendicular and is more common in men. A 69-year-old woman presented with leg pain. MRI revealed an 8.6x5.8x5.5 cm intramedullary lesion in the proximal tibia, causing a pathological fracture. Biopsy confirmed DLBCL, germinal center subtype, with immunohistochemistry positive for CD10, CD20, PAX5, CD45, BCL2, BCL6, and c-Myc (40%). PET scan showed no uptake beyond the primary lesion, but indicated malignant lymphadenopathy in the right popliteal and inguinal regions. The patient underwent 6 cycles of R-CHOP chemotherapy (rituximab, cyclophosphamide, doxorubicin, vincristine, prednisone). A repeat PET scan showed diminished uptake in the primary lesion area, and a biopsy revealed no evidence of lymphoma. She then received consolidative radiation, and a PET scan 1 month later showed decreased residual uptake, likely due to healing rather than malignancy. At this point, she was considered disease-free. Approximately 6 months later, the patient developed a painful nonhealing ulcer on her right lower extremity over the initial lesion area. Punch biopsy revealed large B-cell lymphoma in subcutaneous tissue and deep dermis, with Mum-1, BCL6, and strong c-Myc expression, suggesting primary cutaneous large B-cell lymphoma, leg type. Another PET scan showed increased uptake in the tibia. The plan is to pursue local radiotherapy with possible chimeric antigen receptor (CAR) T-cell therapy in the future for early relapse. Primary lymphomas of the bone are a rare subtype, with the tibia affected in about 17% of cases and a recurrence rate of 9.8%. No cases of recurrence in the skin after the bone being the primary site have been reported. This case highlights the unique presentation and recurrence pattern of PLB, emphasizing the importance of vigilant follow-up and innovative treatments such as CAR T-cell therapy.