Discrimination of chronic lymphocytic leukemia (CLL) and CLL/PL by cytomorphology can clearly be correlated to specific genetic markers as investigated by interphase fluorescence in situ hybridization (FISH).

Although interphase fluorescence in situ hybridization (FISH) is routinely used in chronic lymphocytic leukemia (CLL), differences in the chromosomal pattern with respect to morphological subtypes of CLL (typical CLL, CLL/PL, PLL) are still under debate. We studied 153 patients with CLL and correlated cytomorphology on peripheral blood stains with FISH analysis and other prognostic markers. The percentage of prolymphocytes was calculated as a continuous variable and followed published thresholds in parallel while being correlated to FISH analysis. Higher percentages of prolymphocytes were associated significantly with deletion of 17p13. Deletion of 17p13 was most frequently observed in patients with more than 30% prolymphocytes. Trisomy 12 was found mainly in cases with 6-30% prolymphocytes. The percentage of prolymphocytes did not correlate with deletions of 11q23 or with 13q14 abnormalities. In conclusion, we suggest that further research focus on the percentage of prolymphocytes in CLL. Doing so, biologically relevant thresholds for the percentages of prolymphocytes in the peripheral blood and their association to underlying genetic markers could be investigated together with other biologically and especially prognostic markers.