Genetic Characteristics and Clinical Outcomes of T-Cell Acute Lymphoblastic Leukemia; Myeloid-Suppressive Therapeutic Approach Based on Allogeneic Hematopoietic Cell Transplantation May Benefit in Early T-Cell Precursor Acute Lymphoblastic Leukemia

Background: Early T-cell precursor acute lymphoblastic leukemia (ETP-ALL) is a recently recognized high-risk subgroup of T-cell ALL. T-cell ALL is characterized by poorer survival outcomes compared to B-cell ALL, but the optimal treatment strategies are not well elucidated yet.

Aim: We performed integrative genetic analyses and tried to find important genetic events in T-cell ALL. We also identified clinical outcomes of T-cell ALL including ETP-ALL subgroup, which were treated with myeloid-suppressive chemotherapy followed by allogeneic hematopoietic cell transplantation (allo-HCT) for post-remission therapy.

Methods: We enrolled 40 adult patients with T-cell ALL for analyses of gene mutations and treatment outcomes. Integrative genetic analyses were performed with massive parallel sequencing for NOTCH1, FBXW7, DNMT3A, PHF6, RUNX1, KRAS, NRAS, PTEN, GATA3, EZH2 and SH2B3, and multiplex ligation-dependent probe amplification (MLPA) for copy number alterations of several genes. Among them, quantification of CDKN2A and CDKN2B mRNA expression was performed by reverse transcription-quantitative polymerase chain reaction (RT-qPCR). All were treated with myeloid-suppressive chemotherapy which consisted of hyper-fractionated cyclophosphamide (300 mg/BSA, every 12 h, days 1-3), vincristine (1.4 mg/BSA, maximum dose 2 mg, days 4 and 11), daunorubicin (45 mg/m², days 4 and 11), and dexamethasone (40 mg, days 1-4 and days 11-14) for remission induction, followed by consolidation with high-dose cytarabine (2 g/BSA, every 12 h, days 1-5) and mitoxantrone (12 mg/BSA, days 1-2). Above two anthracycline-intensified regimens were alternatively used for further consolidation. For patients not in complete remission (CR), mitoxantrone (12 mg/BSA, d 1-4), cytarabine (2 g/BSA, every 12 h, d 1-4) and etoposide (100 mg/BSA, d 5-7) were used for reinduction. Our strategy for T-cell ALL in CR was to offer allo-HCT according to the donor availability.

Results: We identified 16 patients with ETP-ALL presenting 1 or more stem cell or myeloid marker with absence of CD1a, CD5, and CD8 expression, and 24 patients with non-ETP-ALL. For genetic mutation profiles between ETP-ALL and non-ETP-ALL, we found DNMT3A was more frequently observed in ETP-ALL (25% vs. 12.5%), while FBXW7 (33.3% vs. 6.2%) and RUNX1 (25.0% vs. 0.0%) were more frequently observed in non-ETP-ALL. We also observed that CDKN2A expression was significantly higher in ETP-ALL (0.053 vs. 0.001, p=0.017). In total, 33 (82.5%) patients achieved CR (24 after induction, 9 after reinduction) and their estimated 5-year overall survival (OS) was 31.3% with median survival of 18.9 months. All 16 (100%) patients with ETP-ALL achieved CR (13 after induction, 3 after reinduction), while non-ETP-ALL in 17 (70.8%, 11 after induction, 6 after reinduction) patients. Estimated 5-year OS of ETP-ALL was 41.7% and non-ETP-ALL was 24.3% (p=0.135). Finally, 12 (75.0%) out of 16 ETP-ALL and 11 (45.8%) out of 24 non-ETP-ALL underwent allo-HCT in CR and their 5-year OS was 55.6% and 45.5%, respectively.

Conclusion: Our data suggested different genetic predisposition between ETP-ALL and non-ETP-ALL and myeloid-suppressive chemotherapy showed a good CR rate in ETP-ALL. Myeloid-suppressive chemotherapy induced CR followed by post-remission allo-HCT can be a good solution for improving poor survival outcome of ETP-ALL.