Plasma Cell Leukemia With Spindle-Cell Morphology and CD22 Positivity on Flow Cytometry.

Plasma cell leukemia (PCL) is a rare and aggressive form of plasma cell neoplasm, defined by the presence of 5% or more circulating plasma cells in peripheral blood in patients diagnosed with plasma cell myeloma. The spindle-cell morphology in PCL is an exceptionally rare feature, adding diagnostic complexity. This case involves a 56-year-old female with PCL, showing elongated spindle-shaped plasma cells in the peripheral blood smear. Bone marrow aspirate and core biopsy confirmed the spindle morphology and extensive atypical plasma cell infiltration, with minimal trilineage hematopoiesis. Flow cytometry analysis revealed CD14, CD22, CD27, CD38, CD81, CD138, and cytoplasmic immunoglobulin lambda chain positivity, with absence of CD19, CD20, CD56, CD117, and Kappa light chains. Spindle cell morphology in plasma cell neoplasms is rare and diagnostically challenging. Additionally, CD22 positivity suggests a unique immunophenotypic profile, potentially representing an intermediate stage between immunoblasts and mature plasma cells. This report documents the first case of CD22-positive PCL with spindle cell morphology.