The clinical course of patients with Ph + ALL has dramatically improved with the current therapies combined with TKIs, including imatinib[10], dasatinib[11] and ponatinib[12]. Meanwhile, molecular remission has recently become a primary goal of treatment. MRD monitoring and BCR/ABL KD mutation are irreplaceable for the successful management of Ph + ALL patients[2]. Nevertheless, 30% of the patients treated with imatinib relapse in a short time interval[13] and there are still some obstructions that remain to be settled on the way to therapy optimization.
Fostered by the high genetic instability of ALL cells, patients with Ph + ALL are highly prone to develop TKI-resistant mutations. The molecular mechanisms are poorly understood up to now and an in-depth evaluation is in need. BCR-ABL mutation has been implicated as a major cause of resistance to TKI therapy[5], which emphasizes the utility and significance of BCR/ABL KD mutation screening analysis.
Clinically universal adjustment in TKI drugs is usually after the occurrence of resistance mutations, with a relatively high possibility of multiple mutations or sustained resistance. The sequential use of TKI could delay the selection of the best treatment. Therefore, the early prediction of BCR-ABL KD acquired mutations is essential. Up to now, few studies focused on the early prediction of acquired BCR/ABL mutation, especially for Ph + ALL.
The most frequent detectable mutation in the Ph + ALL imatinib-resistant in our study is T315I (54.7%), E225K(18.9%) and Y253H (5.7%), which is consistent with the earlier reports[5, 14]. Second-generation TKIs have increased therapeutic effect and have much fewer insensitive mutations [15, 16]. However, sequential treatment by different TKIs may favor the accumulation of multiple mutations and the majority of dasatinib-resistant patients harbor “compound” mutations[17]. The T315I mutation is still a tough enemy for second-generation TKIs and its proportion of dasatinib-resistant genetic alterations (57.1%) has even increased in this research. It revealed the limitation of the efficacy of subsequent treatments. The selected choice of ponatinib and blinatumomab may bring benefits to relapsed Ph + ALL patients.
Therefore, we retrospectively analyzed clinical, cytogenetic, hematological and molecular data collected from 235 Ph + ALL patients and identified high white blood cell count for predicting the ABL1 KD mutation. Previous studies show that high WBC count at diagnosis was a strong prognostic factor associated with a poor outcome in Ph + ALL[18, 19]. Higher WBC count was considered as an independent risk of resistance to TKI in patients with Ph + ALL and an arbitrary cutoff of 17× 109 WBCs/L was calculated in this research.
The allo-HSCT has long been demonstrated to be effective for Ph + ALL patients [20, 21]. However, this approach has become controversial with the application of more potent TKIs, as well as more precise methods for monitoring MRD [22]. Daver et al. found that there was no survival advantage in patients aged 41 to 60 years receiving imatinib plus chemotherapy followed by allo-HSCT[23]. Raising attention towards a risk-modeled allotransplantation strategy could be predicted. Our results indicated that patients with a low-risk of BCR-ABL mutation could be candidates for TKI in combination with chemotherapy without the transplant. In other subgroups, allo-HSCT still confers superior survival for Ph + ALL patients compared with pure TKIs combined chemotherapy. Nevertheless, it represents a tentative step of an attempt to “free- allo-HSCT approaches” in Ph + ALL.
The study has limitations due to its retrospective nature; Patients without achieving MMR after first induced chemotherapy are more prone to occur resistance mutation in univariate(P = 0.053) but not in multivariable logistic regression analysis(P = 0.121). In the future, larger-scale researches or an in-depth evaluation of molecular response need to be carried out.