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A 55-year-old man with a history of multiple myeloma and being treated with daratumumab, bortezomib, lenalidomide, and dexamethasone was admitted due to increasing fatigue and weakness. Laboratory tests revealed leukocytosis (11.3 × 10⁹/L), anemia (83 g/L), thrombocytopenia (19 × 10⁹/L), high lactate dehydrogenase (3500 U/L), elevated blood urea nitrogen (30.3 mg/dL), and normal serum calcium level. Positron emission tomography-computed tomography showed extensive 18-F fluorodeoxyglucose avid bone lesions. Peripheral blood smear showed 28% blastoid cells with scant cytoplasm and fine chromatin (panel A, Wright-Giemsa stain, 100× lens objective). Bone marrow aspirate revealed 71% blastoid cells (panel B, original magnification ×50). Bone marrow biopsy exhibited sheets of blastoid cells (panel C, hematoxylin and eosin stain, original magnification ×40, inset ×100), which were positive for CD138 (panel D, original magnification ×40) and P53 (panel E, original magnification ×40) and negative for Epstein-Barr virus–encoded RNA in situ hybridization (panel F, original magnification ×40). Flow cytometry (panels G-K) identified 80% of cells in the “blast” gate (in red) with an immunophenotype of CD19⁺/CD20⁺/CD10 partial⁺/CD138⁺/CD38⁺/surface κ positive/CD34⁻/CD117⁻/myeloperoxidase negative/CD3⁻/CD56⁻/terminal deoxynucleotidyltransferase negative/λ negative. Cytogenetics showed a complex karyotype. Fluorescence in situ hybridization was positive for IGH::CCND1 rearrangement, TP53 deletion, and 13q14.3 deletion.

Plasma cell leukemia can present with an unusual morphology, like the blastoid morphology in the current case. Hence, it is important to use comprehensive diagnostic modalities during patient workup to avoid misdiagnosis.

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