Minimal Residual Disease (MRD) Analysis in Acute Myeloid Leukemia (AML) with Favorable Cytogenetics [t(8;21) and inv(16)] by Real Time PCR(RT-PCR) and Flow Cytometry (FC).

Objectives: To analyze MRD in 65 patients (pts) with good prognosis AML: 30 t(8;21) and 35 inv(16), using both FC and RT-PCR, and to investigate the prognostic value of MRD in the pts outcome.

Methods: MRD was monitored in CR pts (n=55) by FC in 101 follow-up samples obtained after various cycles of treatment, as follows: 40 post-induction (ind), 30 post-intensification (int) and 31 at the end of treatment (ttm), and by RT-PCR in 76 samples: 31, 23 and 22, respectively. In 35 pts the two techniques were applied at the same time of the ttm. MRD by FC was assessed using fixed combinations of three monoclonal antibodies. AML1/ETO and CBFb/MYH11 were analyzed following the BIOMED protocol.

Results: Twenty-seven percent (n=15) of CR pts relapsed: 6 with t(8;21) and 9 with inv(16). The mean MRD by FC was 1.1% after ind, 0.2% after int and 0.1% at the end of ttm. At the end of ttm, the MRD detected by FC in relapsed and not relapsed pts were significativaly different: 0.3% vs 0.08% (p=0.002). By RT-PCR, the mean of fusion transcript copies/ablx10⁴ differed between relapsed and nonrelapsed pts: 2385 vs 122 (p=0.001) after ind, 56 vs 7.6 after int (p=0.0001) and 75 vs 3.3 (p=0.0001) at the end of ttm. Relapses were more commonly observed in those pts with FC MRD level >0.1% at the end of ttm than in pts with ≤0.1%: 50% vs 12% (p=ns); likewise, using RT-PCR, a cutoff level of >10 copies at the end of ttm correlated with high risk of relapse: 80% of pts with RT-PCR >10 relapsed compared to 12% of pts with levels <10 (p=0.009). The overall survival (OS) probability was 86% for pts with CF MRD ≤0.1 at the end of ttm and 0% for pts with MRD >0.1 (p=0.1) and the leukemia free survival (LFS) was 78% and 44%, respectively (p=0.05). For pts with RT-PCR ≤10 at the end of ttm, the OS was 100% and for pts with RT-PCR >10 it was 30% (p=0.007) and the LFS was 87% and 20%, respectively (p=0.001). MRD was identified after ind in 55% of relapsed pts and at the end of ttm in 83% of relapsed pts. Only 1 pt (1/13) with FC MRD <0.1 and RT-PCR <10 at the end of ttm relapsed. For patients in complete remission, the mean copy level of chimeric transcript was higher for pts with t(8;21) than for those with inv(16): 30.2 vs 17.4 (p=0.0001).

Comments: In tandem analysis of MRD by FC and RT-PCR could improve MRD detection in AML pts.