Short communication Detection of chromosomal abnormalities in chronic lymphocytic leukemia increased by interphase fluorescence in situ hybridization in tetradecanoylphorbol acetateestimulated peripheral blood cells

Interphase fluorescent in situ hybridization on unstimulated peripheral blood mononuclear cells (I- FISH-PBMC) is used to detect chromosomal abnormalities such as 11q� , 13q� , 17p� , and trisomy 12 in chronic lymphocytic leukemia (CLL). A total of 56 samples from 49 patients with CLL were studied using commercially available probes for chromosome regions 11q22.3 (ATM), 13q14 (13S272), 17p13 (p53) and 12 centromere (D12Z3). We compared the results obtained with I-FISH-PBMC and those with I-FISH on TPA (tetradecanoylphorbol acetate; phorbol-12- myristate-13-acetate) stimulated peripheral blood cells (I-FISH-TPA) used for conventional cytoge- netics, to evaluate the usefulness of I-FISH-TPA. The proportion of abnormal nuclei obtained with the I-FISH-TPA was higher than that found with I-FISH-PBMC (P ! 0.001). Consequently, 15 cases with a negative or borderline result with I-FISH-PBMC became positive with I-FISH-TPA for 11q� (n 5 2), 13q� (n 5 9), and trisomy 12 (n 5 4). In all but one of these, chromosomal abnormalities were confirmed by either metaphase FISH or conventional G-banding. Detection of cytogenetic aberrations thus increased from 51% with I-FISH-PBMC to 78% with I-FISH- TPA. Notably, all 15 of the cases that reached the diagnostic thresholds for 11q� , 13q� , and tri- somy 12 had a slight lymphocytosis. An absolute lymphocyte count !8.7 � 10 9 /L was found to be the critical threshold (P 5 0.037) below which I-FISH-TPA rather than I-FISH-PBMC should be performed. Not only could I-FISH-TPA detect a higher proportion of abnormal interphase nuclei, but it could also identify abnormal CLL cases that might be overlooked with use of I-FISH-PBMC, especially those with low absolute lymphocyte counts. I-FISH-TPA is thus a reliable technique for