Impact of biological and genetic features of leukemic cells on the occurrence of “shark fins” in the WPC channel scattergrams of the Sysmex XN hematology analyzers in patients with chronic lymphocytic leukemia

OBJECTIVES: In patients with chronic lymphocytic leukemia (CLL), the white progenitor cell (WPC) channel of the Sysmex XN hematology analyzers typically shows a varying proportion of cells in the upper left field of the scattergram, resembling the shape of shark fins. The underlying mechanism causing this phenomenon has not been elucidated so far. In this study we evaluated biological and/or genetic features of CLL cells as a potential background of the "shark fins". METHODS: Automated blood counts and WPC scattergrams of 95 CLL patients were analyzed. The scattergrams were examined for the presence, count and percentage of cells in the "shark fins" using a flow cytometry software. Potential influencing factors on the occurrence of the "shark fin" cells were statistically tested by Spearman correlation. RESULTS: The lymphocyte count was identified as a highly statistically significant predictor of "shark fins" (p<0.0001). Absence of del(17p) (p=0.02), unmutated TP53 (p=0.01), mutated IGHV (p=0.03) and the percentage of smudge cells in peripheral blood smears (p=0.04) showed a statistically significant positive influence on the percentage of cells in the "shark fins" after adjustment for the lymphocyte count. No significant effect was observed for age, sex, del(13q), del(11q), trisomy 12 and treatment. CONCLUSIONS: We identified the lymphocyte count, the absence of TP53 mutations and del(17p), a mutated IGHV and the proportion of smudge cells as significant influences on the appearance of "shark fin" cells. Our findings indicate an impact of biological and genetic properties of the leukemic cells on the formation of "shark fins".