Monitoring Response to Imatinib by Fluorescence In Situ Hybridization (FISH) and Real-Time Quantitative Polymerase Chain Reaction (RQ-PCR) in Chronic Myeloid Leukemia (CML) Patients in Chronic Phase. Experience of Argentina and Uruguay.

Introduction: The evaluation of response to imatinib in CML patients (pts) as guide to clinical management is undergoing substantial changes of criteria. The degree of reduction of total leukemia cell mass by imatinib as measured by FISH and RQ-PCR studies, correlates with progression-free survival. Therapeutic decisions, as dose scalation, is mandatory in pts with rising level of bcr/abl transcripts.

Purpose: To determine the potential of RQ-PCR to predict the duration of response in pts in complete cytogenetic remission (CCyR).

Patients and Methods: A total of 160 CML pts in first chronic phase, in CCyR treated with imatinib 400mg daily were studied prospectively since November 2005 (147 pts from 30 hematology centers in Argentina and 13 pts from 2 centers in Uruguay). According to previous treatment they were divided in two groups: 83 pts (51%) received as first line treatment IFN/Cytarabine and 77 pts (49%) received imatinib as first line. According to Sokal Index, 72% were low risk, 19% intermediate risk and 9% high risk. At baseline all pts were first evaluated by FISH and RQ-PCR under EAC program protocol and recommendations of T.P. Hughes, et al (Blood 108:28–37, 2006). Only RQ-PCR is being performed at 6 and 18 months from the beginning of the study. The median duration since beginning with imatinib treatment was 28 months (range 6–58).

Results: At the time of first RQ-PCR evaluation, 93% had undetectable bcr/abl fusion gene by FISH and 7% had low level FISH positivity ( 0,1 – 5%). The distribution of the type of molecular responses (MR) in the 160 pts was: Complete (CMR)≥4 log red, U/<0.01% bcr-abl/c-abl : 23%; Major (MaMR) ≥ 3log red, <0,1%bcr-abl/c-abl : 17%; Minor (MiMR) >2 log red, 1–0,1 % bcr-abl/c-abl : 34%; MiMR < 2log red, 10–1% bcr-abl/c-abl : 15%; Nule (NuMR) <1 log red, > 10%bcr-abl/c-abl : 11%. Pts with Fish (+) showed association with MiMR. Thirty eight percent of pts with a follow-up between 6–24 months since the beginning of imatinib treatment achieved MaMR and CMR, similar rate as the observed in the group with > 24 months on imatinib (42%). Up to July 2006, 53 pts underwent a 2nd RQ-PCR evaluation at 6 months: 15% of pts improved molecular response, 68% maintained it while 17% showed worse response. The 87.5% of pts with decreasing bcr-abl transcripts level at 2nd evaluation corresponded to imatinib treatment as first line. The 78% of pts with rising levels at 2nd evaluation showed MiMR at beginning of this study. Up to now, no pts showed hematological relapse.

Conclusion: This is an on-going study in CML pts in CCyR, where 93% showed a negative FISH study, and 7% had low FISH positivity. By RQ-PCR, 40% of pts presented CMR or MaMR (≥3 log red). In 2nd RQ-PCR evaluation, 83% of pts improved or maintained the molecular response. Up to now all pts remain in hematological remission.