#00064074

A 30-year-old male with no significant past medical history presented with fatigue, night sweats, and weight loss and was found to have normocytic anemia (Hgb 10.3 g/dL), elevated LDH (1019 U/L), and hypercalcemia (10.7 mg/dL). Hematoxylin and eosin stain (40X) of the bone marrow core biopsy showed extensive tumor necrosis and focal clusters of viable immature blasts of medium size with round nuclear contour, a high nuclear to cytoplasmic ratio, fine chromatin, and scant cytoplasm (A). Immunohistochemistry (all at 40X) demonstrated that the lymphoblasts stained positive for CD19 (B), CD5 (C), and TdT (D) but were negative for CD20 (E) and CD3 (F).  Flow cytometry analysis identified an expanded lymphoblast population (green) that represented 23.7% of total cells in the side scatter versus CD45 gate (G). The lymphoblast population was double positive for both CD19 and CD5 (H). Additionally, lymphoblasts were positive for CD10, CD38, CD58 and HLA-DR, but negative for surface immunoglobulin light chain expression, myeloid or other T cell markers (data not shown). Together, these findings are most consistent with a diagnosis of B-cell acute lymphoblastic leukemia (B-ALL) with atypical CD5 antigen expression, a rare subcategory of B-ALL associated with poor prognosis.¹

1.     Ye MT, Zhu J, Luo DX, et al. B-Lymphoblastic Leukemia With Aberrant CD5 Expression. Am J Clin Pathol. 2021;156(4):586-595. doi:10.1093/ajcp/aqaa269