Post-Remission Treatment with Chemotherapy or Allogeneic Hematopoietic Stem Cell Transplantation (alloHSCT) of High-Risk (HR) Philadelphia Chromosome-Negative (Ph-neg) Adult Acute Lymphoblastic Leukemia (ALL) According to Minimal Residual Disease (MRD). Preliminary Results of the Pethema ALL-HR-11 Trial

Introduction: Recent studies have shown that young to middle-aged adults who receive a pediatric-inspired chemotherapy regimen for treatment of Ph-neg ALL do not appear to require an alloHSCT if they achieve good response on MRD testing after induction therapy. Patients (pts) who are not good MRD responders achieve better outcomes with alloHSCT than their counterparts who do not receive alloHSCT. However, it is not clear if this approach can be translated to adult ALL pts with HR features at baseline. The aim of the prospective ALL-HR-11 trial from the Spanish PETHEMA Group was to evaluate the response to a differentiated post-induction therapy (chemotherapy or alloHSCT) according to MRD levels (assessed by 8-color, centrally-performed flow cytometry at the end of induction-week 5- and consolidation therapy-week 17-) in HR Ph-neg adult ALL patients. Patients and methods: HR ALL included one or more of the following parameters at baseline: age 30-60 yr, WBC count >30x10⁹/L for B-cell precursor ALL or >100x10⁹/L for thymic T-ALL, pro-B, early or mature T-ALL, 11q23 or MLL rearrangements or complex karyotype. Induction therapy included vincristine, prednisone, daunorubicin and asparaginase (E coli native or PEG according to center availability) for 4 weeks (Induction-1). FLAG-Ida was administered as intensified induction (Induction-2) in pts not achieving CR or those in CR with MRD≥0.1% at the end of induction. For pts in CR and MRD<0.1% early consolidation therapy included 3 cycles with rotating cytotoxic drugs with high-dose methotrexate, high-dose ARA-C and high-dose asparaginase (E coli native or PEG). These pts continued with delayed consolidation (identical to that of early consolidation) followed by maintenance therapy up to 2 yr. in CR if MRD levels after consolidation were <0.01%, otherwise they were assigned to alloHSCT. Pts in CR after Induction-2 received one consolidation cycle and were assigned to alloHSCT. Results: On June 2015, 115 HR ALL pts were evaluable [mean (SD) age 38(13) yr, 67 males, 80/114 precursor B-ALL, 34/114 T-ALL, WBC count 56(96) x10⁹/L]. Results of Induction-1: therapy-related death: 4(4%), resistance: 11 (10%), CR: 95(86%). MRD<0.1% at the end of induction was observed in 75% of CR patients. Induction-2 was administered to 33 patients (no CR: 11, CR and MRD≥0.1%: 22). No differences in the CR rate or in the rate of MRD clearance after induction were observed according to the type of asparaginase administered, although significantly increased hepatic toxicity in consolidation was observed in patients treated with PEG-asparaginase. The 2-yr DFS and OS probabilities for whole series were 51%±18% and 62%±13%. By intention-to treat after Induction-1 36 pts were assigned to alloHSCT and 68 to delayed consolidation and maintenance. The 2-yr DFS and OS probabilities were 54%±25% and 49%±20%, respectively, for pts assigned to alloHSCT, and 50%±22% and 73%±17%, respectively, for those assigned to chemotherapy (P=0.002 for OS comparison). Patients with MRD<0.1% at the end of induction and <0.01% at the end of consolidation (n=51) showed a 2-yr DFS and OS of 55%±25% and 81%±18%, respectively. Conclusions: The preliminary results of this trial, in which the post-induction therapy decision is only based on MRD results, suggest that in HR, Ph-neg adult ALL pts with adequate MRD response after induction and after consolidation the results of therapy are not hampered by avoiding alloHSCT. Supported by grants RD12/0036/0029 (RTICC, FEDER), PI14/01971 FIS, Instituto Carlos III, and SGR225 (GRE), Spain