Imatinib Mesylate Therapy in Late Ph+ Chronic Myeloid Leukemia Patients in Stable Complete Cytogenetic Response after Interferon-Alpha Results in a Very High Complete Molecular Response Rate.

Imatinib mesylate was given to 26 Philadelphia positive (Ph+) chronic myeloid leukemia (CML) patients who were in late chronic phase (CP) and in stable complete cytogenetic response (CCR) after interferon-alfa (IFN-α), but showed persistent positive residual disease at PCR analysis under this treatment. At diagnosis median age was 40 years (range 21–64) and according to Sokal’s score, 18 patients were low risk and 8 were intermediate risk. Median IFN treatment was 88 mo.s (range 15–202) and median CCR duration was 73 mo.s (range 10–148). Imatinib was administered at the standard dose of 400 mg/die, after stopping IFN for 1 week. Residual disease was measured on bone marrow (BM) cells at baseline, before starting Imatinib, at 3, 6, 12, 18 mo.s and at the last follow-up (median 32 mo.s, range 21–49), by assaying BCR-ABL transcripts using quantitative PCR (RQ-PCR). The copy number (CN) of BCR/ABL and ABL transcript were derived by the interpolation of CT values to the appropriate standard curve, and the result, for each sample, was expressed as ratio of BCR/ABL mRNA copies to ABL mRNA x 100 (normalized copy number - NCN).

Imatinib treatment resulted in a progressive and consistent decline of residual disease in all but one patient, from a median of 0.89 at baseline to 0.01 at the end of follow-up. Major molecular response (BCR/ABL levels <0.1) was reached in 20 patients (77%) and BCR/ABL transcripts were undetectable in 13 (50%). Achievement of molecular response was significantly correlated with post-IFN baseline transcript level (mean 1.194 for patients achieving complete molecular response vs 18,97 for those who did not; p<0.001), but not with other clinical/biological patient characteristics. In all patients, imatinib was well tolerated with no side effects requiring drug dose reduction or dose discontinuation.

Albeit obtained from an unusual subset of selected patients with favourable prognosis, and likely particularly sensitive to imatinib, present results confirm the efficacy of combining Imatinib and IFN-α and further support investigating treatment approaches employing these two drugs.