Monitoring Minimal Residual Disease by Quantitative PCR in Chronic Myeloid Leukemia Patients in Complete Cytogenetic Remission

Abstract

The landscape of chronic myeloid leukemia (CML) has radically changed since the introduction of tyrosine kinase inhibitor (TKI), imatinib (IM), now considered as standard therapy. Although excellent cytogenetic responses are obtained, minimal residual disease still persists in a proportion of patients (pts) when measured by serial molecular monitoring by quantitative real-time polymerase chain reaction (RQ-PCR) to measure BCR-ABL transcript levels (Baccarani M et al. Blood2006; 108:1809–20). We monitored BCR-ABL transcript levels by RQ-PCR in 176 chronic phase (CP) –complete cytogenetic response (CCyR) CML pts treated with IM. Median follow-up from start of therapy with IM was 35 (6–80) months. Pts were recruited from 33 centers in Argentina and 2 in Uruguay. Median follow up from the first assessment at our Institution was 18 (6–32) months. Seventy nine patients (45%) had received interferon as 1st line prior to IM and 97/176 (55%) pts received imatinib as 1st line. Eighty eight percent (155/176) pts had received IM 400mg/d and 12% (21/176) 600–800mg at study initiation. Fifty four percent presented with low Sokal score at diagnosis. Peripheral blood samples were tested by RQPCR every 6 months. Major molecular response (MMR) was defined as BCR-ABL/ABL ratio of <0,1% on the Internationale Scale. Rise in transcript levels was immediately reconfirmed. Cytogenetic and mutational analyses were performed if rise in transcripts was confirmed. Overall, 48% had MMR at the initial evaluation (baseline), and this increased to 57% at last follow-up (month 18). No patient with MMR achievement lost CCyR. Only 5 pts lost CCyR, never having achieved MMR (p=0.01). All patients could be divided in 3 groups according to transcript level outcome: 61% decline (at least 1 log reduction of BCR-ABL/ABL ratio), 27% stable (no log variation), 13% rise (increasing 1 log of BCR-ABL/ABL ratio). Among 136 pts with follow up at month 18, we observed (Table 1): Molecular Response At baseline Decline in transcript levels %(pts) Stable transcript levels %(pts) Rise in transcript levels %(pts) Total %(pts) CMR: complete molecular response, U: undetectable CMR ≥ 4 log red <0,01%/U MMR ≥ 3 log red < 0,1% (N:60) 20(12) 63(38) 17(10) 44(60) No MMR > 0,1% (N:76) 47(36) 47(36) 5(4) 56(76) Total 35 (48) 55(74) 10(14) 100(136) From the group of pts with rise in transcript levels, 5 pts lost CCyR, none lost complete hematologic response. Overall, 5%(9/176) pts eventually changed therapy to a 2nd generation TKI: 5 pts with cytogenetic relapse and 4 pts with increase in transcript levels. Our results confirm that molecular responses continue improving over time and a significant number of pts achieve undetectable transcript levels with continued imatinib therapy. Achievement of MMR is associated with sustained cytogenetic response. These results emphasize the validity and feasibility of molecular monitoring in all areas of the world.