Clinical Significance Of Different BCR/ABL Transcripts And The Transcript Evolution At Relapse In Philadelphia-positive B-ALL In The Era Of Tyrosine Kinase Inhibitors

Objective:Ph chromosome-positive B-lineage acute lymphoblastic leukemia(Ph + B-ALL)has significantly improved its prognosis through the application of tyrosine kinases inhibition(TKIs),but a higher cumulative relapse rate is becoming a huge barrier in the treatment of these patients.In our previous work,we found that the type of BCR/ABL transcript was different between diagnosis and relapse in some Ph+ B-ALL patients.We speculate that the type and evolution of BCR/ABL transcript may be involved in the relapse of the disease.Therefore,the purpose of this study was to investigate the distribution of different transcripts in Ph+ B-ALL patients at diagnosis and their clinical characteristics and prognosis;analyze the pattern and clinical significance of BCR/ABL transcript evolution in relapsed Ph+ B-ALL patients.Methods:1.Collecting bone marrow samples of matched diagnosis,remission and relapse samples in 44 Ph+ B-ALL patients and extracting RNA for preservation.2.Real-time fluorescent quantitative PCR(RT-qPCR)was performed to detect BCR/ABL-P190 and P210 transcripts in Ph+ B-ALL patients.Samples with undetectable P210 or P190 were further validated by droplet digital PCR(dd-PCR).3.Sanger sequencing was used to detect the point mutation of ABL kinase region in relapsed Ph+ B-ALL patients.Results:1.Among 44 Ph+ B-ALL patients,RT-qPCR combined with dd-PCR was performed to detected the type of BCR/ABL transcripts at diagnosis: P190 in 21 cases(47.73%),P210 in 10 cases(22.73%),13 cases(29.55%)co-expressed P190 and P210.The BCR/ABL transcripts were negative by RT-qPCR but positive by dd-PCR in eight patients.2.Compared with patients expressing P190 or P210 alone,patients with co-expressing P190 and P210 had higher bone marrow blasts counts at diagnosis(P =0.016),lower complete remission after the first induction chemotherapy(CR1)rate(P =0.002),lower total complete remission(CR)rate(P = 0.029)and higher overall mortality(P = 0.021).3.Among 44 cases of Ph+ B-ALL,24(54.55%)cases relapsed.The type of BCR/ABL transcripts were: P190 in 12 cases(50.0%),P210 in 3 cases(12.5%),and co-expressed P190 and P210 in 9 cases(37.5%).Compared with patients in the non-relapsed group,the positive rate of CD13 was higher in relapsed patients(P = 0.048),EFS was shorter(P < 0.001),and OS was shorter(P = 0.045).There were no significant differences in other indicators between the relapsed group and the non-relapsed group.4.Of the 24 patients with relapsed Ph+ B-ALL,9(37.5%)had transcript evolution during relapse.Compared with BCR/ABL transcripts at diagnosis,the evolution of BCR/ABL transcripts at relapse can be attributed to three patterns,the emergence of new transcript,the disappearance of minor transcript,and the transformation of primary and minor transcripts.5.In relapsed Ph+ B-ALL patients,compared with the non-BCR/ABL transcript evolution group,the BCR/ABL transcript evolution group had higher longer EFS(P =0.023),Relapse-free survival after first relapse(RFS)and OS showed shorter tendency.Removed 10 patients(41.7%)with point mutations in the ABL kinase region after relapse and reanalyzed the prognosis of the patients in the BCR/ABL transcript evolution group and non-transcript evolution group,similar conclusions were obtained.Conclusion:1.In diagnosed Ph+ B-ALL patients,compared with patients with single expression of P190 or P210,patients with co-expression of P190 and P210 have lower complete remission rates,higher mortality,and showed poor prognosis.2.Compared with non-relapsed patients,relapsed patients have poor prognosis with shorter EFS and shorter OS.3.Ph+ B-ALL patients have the BCR/ABL transcript evolution at relapse,which can be attributed to three evolution patterns.The transcripts evolution need a long time to obtain,and there is a tendency of poor prognosis after occurring transcripts evolution.