To the Editor: The t(9;22)(q34;q11) (Philadelphia chromosome [Ph]) balanced translocation results in fusion of the BCR gene at 22q11 with cytoplasmic tyrosine kinase gene ABL1 and plays an essential role in leukemic transformation. The Ph is an infrequent finding in de novo acute myeloid leukemia (AML), approximately 0.5–3% of newly diagnosed patients. The World Health Organization (WHO) recently released a revised version of the Classification of Hematopoietic and Lymphoid Malignancies, a new provisional category of AML with BCR-ABL1 was added to recognize these rare Ph+ AML cases that could benefit from tyrosine-kinase inhibitor (TKI) therapy. It is required to enlarge the sample size and research the molecular or genomic features to increase the argument in favor of Ph+ AML as a real entity.
A total of 5402 Chinese patients with de novo AML were identified from the database of the Department of Hematopathology at Medical University of Suzhou and Affiliated Changzhou Second Hospital of Nanjing Medical University for the period from September 2005 to October 2016. Ph+ AML was defined as cases fulfilling the current WHO criteria for AML that bore the t(9;22)(q34;q11) or variant (9;22) translocation on bone marrow cytogenetics, had no history of chronic or accelerated phase chronic myeloid leukemia (CML) before diagnosis, no evidence of a CML-like picture following therapy for AML, no presence of splenomegaly or basophilia (defined as >2% of basophils in peripheral blood) suggestive of a myeloproliferative neoplasm, and no history of chemotherapy and/or radiation therapy. Cases fulfilling diagnostic criteria of the 2016 WHO classification for acute ambiguous lineage leukemia were also excluded from the study.
The overall incidence of de novo Ph+ AML among all cases of AML was 0.22% (12/5402). The frequency (0.22%) is lower than the previous study; we believe that the stringent exclusion criteria used may explain the lower frequency.
Next-generation sequencing (NGS) was available in seven patients using a custom-designed 49 genes' panel (Ion S5™ System, Thermo Fisher, San Diego, CA, USA), including the entire coding region of ASXL1, ASXL2, BCOR, BCORL1, BIRC3, BRAF, CALR, CBL, CDKN2A, CSF3R, CSMD1, DNMT3A, ETNK1, ETV6, EZH2, FBXW7, FLT3, GATA2, IDH1, IDH2, IL7R, JAK1, JAK2, JAK3, KIT, KRAS, MPL, MYD88, NOTCH1, NRAS, PAX5, PDGFRA, PDGFRB, PHF6, PIGA, PTEN, PTPN11, RUNX1, SETBP1, SETD2, SF3B1, SH2B3, SRSF2, STAG2, TET2, TP53, U2AF1, WT1, and ZRSR2, with a median depth of ×2000. FLT3-ITD, NPM1, and CEBPA mutations were detected by DNA-based polymerase chain reaction.
Overall, six patients harbored at least one mutation. The frequently mutated genes, in order of mutation prevalence, were RUNX1 (3/7), IDH1 (2/7), ASXL1 (1/7), ASXL2 (1/7), NRAS (1/7), KRAS (1/7), TET2 (1/7), DNMT3A (1/7), and CSMD1 (1/7). Detailed data are summarized in Table 1.
Clinical data were available in 12 patients with follow-up extending from 45 days to 11 years after diagnosis, and the median survival time was 17.5 months. Among three RUNX1-mutated patients, two patients achieved complete remission (CR) and one patient did not have any response to traditional chemotherapy. We found no difference in CR rate between patients with RUNX1mut and RUNX1wild type (2/3 vs. 3/4, P = 0.809). Six of the seven patients received allogeneic hematopoietic stem cell transplantation (allo-SCT) in first CR and one patient (Case No. 8) received allo-SCT in partial remission condition. Among these seven patients, six patients, except the case No. 12, received TKI at diagnosis. All patients with RUNX1 mutations eventually relapsed and were trended toward reduced overall survival (OS, median: 19 vs. 62 months) as compared to patients with RUNX1 wild type. Interestingly, the patient (Case No. 12) who had IDH1R132 as a solitary abnormality achieved rapidly remission after chemotherapy; subsequently, the allo-SCT was treated and the disease-free survival time had been beyond 10 years; notably, the TKI therapy was not employed.
Numerous data confirmed that RUNX1 mutation was a significant predictor for resistance to standard chemotherapy and for inferior survival. A portion (3/7) of this Ph+ AML cohort was found to carry RUNX1 mutations, strong higher than previously published data in other series. RUNX1 mutations have been described not to be able per se to cause full-blown leukemia; the coexistence of BCR-ABL1 and RUNX1 mutations in this study raises the possibility of synergistic effect between two genetic alterations on leukemogenesis. Similar to what has been reported in adult AML patients, our observations suggest that RUNX1 mutations may also be associated with poor outcome in Ph+ AML, which could be explained by an association with reduced OS. However, we could not draw a definitive conclusion because of the small number of Ph+ AML patients.
The frequency of IDH mutations is clearly low in CML, and there were no reports in Ph+ AML patients except these our cases. Our data demonstrated that the patient who had IDH1R132 as a solitary molecular abnormality remained in CR at the most recent follow-up in October 2016 (beyond 10 years after allo-SCT), he received no TKI. Recent data showed that Ph+ AML patients could benefit from the added therapy with TKI; however, it was important to note that massive mutational screening by NGS had not been performed, a novel concept based on NGS is critically needed.
In summary, our identification of only 12 Ph+ AML cases in an 11-year period at two large institutions confirms that this is an extremely rare disease. Ph+ AML cases carried RUNX1 mutations at a higher frequency to that in AML patients in general, and all these patients died of relapse even undergoing allo-SCT. On the contrary, seemingly Ph+ AML patient with mutation in IDH1R132 could be remissioned by allo-SCT, even without TKI. Further bigger studies utilizing NGS methods may provide guidance for Ph+ AML prognostic stratification and clinical management.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form, the patients have given their consent for their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
This work was supported by grants from the National Natural Science funds (No. 81500103), Natural Science Foundation of Jiangsu Province (BK-20151230), and the high-level medical talents training project (No. 2016CZLJ027).
Conflicts of interest
There are no conflicts of interest.
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Edited by: Li-Shao Guo