Comparison of Cytogenetics and Interphase Fluorescence In Situ Hybridization in Newly Diagnosed Ph+ Chronic Myeloid Leukemia Patients Treated with Imatinib Mesylate. A Study by the GIMEMA Working Party on CML. On Behalf of GWP on CML.

To asses cytogenetic pattern of early diagnosed chronic phase chronic myeloid leukemia (CML) patients and to evaluate the role of either conventional (CC) and molecular cytogenetics in three multicentric studies, karyotype and interphase fluorescence in situ hybridization (FISH) analyses were performed in 372 enrolled patients between April 2004 and July 2005 by the GIMEMA CML Working Party (WP). Local investigator laboratories (25 labs) or WP reference labs (12 labs) performed both analyses. Cytogenetic examinations was performed at baseline; after 6 and 12 months of imatinib treatment; thereafter every 6 months and in case of failure or disease progression. At the baseline, 257 patients have been studied and 237 (92%) are valuable for both analyses (CC and FISH). Additional abnormalities in Ph+ clone have been observed in 12 patients (5%). Moreover, 18 (8%) cases showed variant Ph translocations and in 23 (10%) patients the derivative of chromosome 9 was deleted. As yet, cytogenetic response (CR) was evaluated in 188 samples and 156 cases were valuable (83%): 20 at 3 months, 101 at 6 months and 35 at 1 year of treatment. One hundred and eighteen (76%) patients achieved complete CR (CCR) established with more than 20 metaphases in 84 cases, meanwhile in 34 CCR cases the number of examined metaphases was lower. In the first group, 70/84 (83%) samples showed absence of bcr/abl rearrangement in FISH, meanwhile 13/84 (16%) carried a low rate of positive cells (1–5%) and the last one showed the rearrangement in 12% of cells. In the latter group, 23/34 (68%) didn’t show any rearrangement in FISH, in 8/34 (24%) the amount of Ph+ cells was low (1–5%), in 2 was higher (7% and 10%) and the last one carried an high rate (72%) of rearranged cells. In this latter case the RCC was evaluated on 10 metaphases. Twenty-three patients in major CR (MCR), but not in CCR, showed retention of persisting Ph+ cells ranging from 2 to 21% in CC study and from 2 to 16% in FISH analysis. Moreover we found a patient with 2% of Ph+ metaphases and 53% of Ph+ cells in FISH: in this case the CC evaluation was established with 10 metaphases. We can suggest there was a good correlation between cytogenetic and FISH tests in terms of the kinetics of disappearance of the bcr/abl rearrangement. FISH is a reliable method to reveal submicroscopic deletions and to monitor the size of the Ph + clone in treated CML patients. However, a good CC analysis remains an excellent approach to the evaluation of response to Imatinib. Moreover it can detect the emergence of other abnormalities in Ph positive or negative clone.