Rare transformation of extramedullary plasmacytoma to plasmablastic myeloma: A case report and diagnostic considerations

Extramedullary plasmacytoma (EMP) is a rare plasma cell malignancy, comprising a small subset of plasma cell neoplasms. It can occur as a solitary lesion in bone (bone plasmacytoma) or soft tissue (extramedullary plasmacytoma). Many clinicians are not yet aware that cases of extramedullary plasmacytoma can be transform into plasmablastic myeloma, which has a poor prognosis. A 35-year-old male presented with progressive weakness and a persistent cough. Clinical examination findings: in the thoracic area showed a lumpy, immobile mass measuring approximately 15 cm was found in the left thoracic region. Imaging showed a destructive mass in the left posterior thoracic wall, measuring 17.72 cm×15.74cm×16.83 cm. Fine Needle Aspiration Biopsy (FNAB) confirmed extramedullary plasmacytoma. Bone marrow aspiration revealed 92% plasmablast cells, suggesting possible transformation to plasmablastic myeloma. Immunophenotyping showed positive for CD138 and CD56, but negative for CD34, CD19, CD20, CD79a, CD33, and CD13. Protein electrophoresis showed monoclonal gammopathy. Transformation of extramedullary plasmacytoma into plasmablastic myeloma is rare but clinically significant. This case emphasizes the importance of thorough diagnostic evaluation, including bone marrow aspiration and immunophenotyping, to detect early disease progression. Immunophenotypic markers, such as CD138 and CD56 positivity with CD34, CD19, and CD20 negativity, aid in diagnosis. Early detection of transformation is crucial for timely treatment due to the aggressive nature of plasmablastic myeloma. This case underscores the need for close collaboration between clinicians and pathologists to ensure early detection of EMP transformation into plasmablastic myeloma. Comprehensive diagnostic workup, including bone marrow aspiration and immunophenotyping, is essential to guide appropriate clinical management