Plasma cell leukemia with soft tissue involvement; reporting a rare case

Plasma cell leukemia (PCL) is a rare aggressive variant of multiple myeloma. PCL is diagnosed when clonal plasma cells constitute more than 20 % of the total circulating leukocytes or when the absolute plasma cell count exceeds 2 × 10⁹ /L. Extramedullary involvement including cavity effusion is frequently seen at the time of diagnosis. However, soft tissue involvement is rarely encountered with only one published case in the English literature. We report a 74-year-old man, who presented with progressive shortness of breath over a few months. Laboratory studies showed leukocytosis (32 × 109 /L) with 26 % peripheral plasmacytoid cells and significantly elevated lactate dehydrogenase (> 2500 U/L). Serum protein electrophoresis detected a monoclonal IgG lambda band. A 7.4 cm left hilar mass, bilateral pleural effusion, and multiple fluorodeoxyglucose (FDG)-avid subcutaneous nodules in the pelvic and gluteal regions were demonstrated on imaging. Gluteal nodule biopsy revealed diffuse infiltrative CD138+ and MUM1+ cells with aberrant CD4, CD30, and BCL2 expression. The Ki-67 proliferation index was 70 %. Bone marrow biopsy showed sheets of atypical plasma cells with lambda-restriction and CD138 and MUM1 expression without cyclin D1 and CD20 expression. These cells comprise approximately 70-80 % of the bone marrow cellularity. A similar immunophenotype was demonstrated in peripheral and bone marrow flow cytometry. Molecular and cytogenetics showed an abnormal clone with a complex karyotype including monosomy 13 and 14q deletion. Overall, these findings are consistent with a plasma cell neoplasm. Our case study illustrates soft tissue involvement in PCL, which is rarely seen.