#00066541

Flow cytometric analysis at the time of clinical progression demonstrates the emergence of a distinct atypical large cell population (ATL,black) with increased forward and side scatter properties, highlighting large-sized cells with increased cellular complexity. The transformed population accounts for approximately 58.9% of analyzed leukocytes, with a concomitant reduction in the background CLL population (red) (11.25%). Immunophenotypically, the transformed cells show altered antigen expression with attenuation of the typical CLL phenotype. The transformed cells demonstrate moderate CD20 expression with dim to negative CD200 expression, along with persistence of light chain restriction, supporting clonal evolution and large cell transformation consistent with Richter transformation.