Prognostic impact of KMT2A‐AFF1‐positivity in 926 BCR‐ABL1‐negative B‐lineage acute lymphoblastic leukemia patients treated in GIMEMA clinical trials since 1996

To the Editor: The impact of KMT2A-AFF1 rearrangement in pediatric-like, minimal residual disease (MRD)-based clinical trials and the effect of transplant in KMT2A-AFF1 ALL are still debated. By analyzing 926 BCR-ABL1-negative ALL treated in GIMEMA (Gruppo Italiano Malattie EMatologiche dell'Adulto) clinical trials since 1996, we documented that KMT2A-AFF1-positive ALL accounting for 10.5% of cases had a significantly shorter survival than KMT2AAFF1-negative (20.3% vs 45.5%, p = 0.003), also after censoring for transplant. Within KMT2A-AFF1-positive patients, the only independent prognostic factor was allogeneic stem cell transplant (ASCT, HR: 0.318, p = 0.002), that confers a survival advantage to KMT2A-AFF1positive patients. The prognosis of adult B-lineage acute lymphoblastic leukemia (B-ALL), thought greatly improved over the years, is still suboptimal with survival rates approaching 50% at 5 years. The only subset that witnessed a dramatic improvement of outcome is BCR-ABL1-positive ALL that benefited from the introduction of tyrosine kinase inhibitors. Within BCR-ABL1-negative ALL, t(4;11)(q21;q23) is the most common chromosomal abnormality, accounting for roughly 10% of adult patients. In ALL the KMT2A-AFF1 fusion gene, derived from t(4;11) (q21;q23), is the most recurrent rearrangement of the promiscuous KMT2A gene and functions as a transcriptional activator. KMT2AAFF1/t(4;11)(q21;q23) leukemia is associated with a pro-B immunophenotype and it is recognized by the major cooperative groups as a subset with a particularly poor outcome. For the latter reason, KMT2A-AFF1-positive ALL patients are managed more intensively and allocated to allogeneic transplant. However, the datasets analyzed so far are too small to draw definitive conclusions on the role of KMT2A-AFF1 in pediatric-like, minimal residual disease (MRD)based clinical trials, and on the impact of transplant in this poor prognostic subgroup. To this respect, in the largest study conducted on patients enrolled in the UKALLXII/ECOG2993 clinical trial including 88 KMT2A-AFF1-positive patients – patients undergoing ASCT had a survival advantage in comparison to those who received chemotherapy, though allograft was not an independent factor in multivariate analysis. The PETHEMA group observed a trend towards a longer CR duration in KMT2A-AFF1 undergoing HSCT vs those receiving chemotherapy. With regards to MRD-based protocols, the GRAALL study showed that KMT2A-AFF1 fusion gene retains prognostic significance in a multivariate model that included MRD as a covariate for cumulative incidence of relapse. Alongside, Issa et al. analyzed the impact of cytogenetic alterations in roughly 400 BCR-ABL1-negative ALL in the context of protocols contemplating MRD quantification. The authors confirmed the negative impact of KMT2A-AFF1-positivity on survival but, in a multivariate model, KMT2A-AFF1 rearrangement was not independently predictive of survival while MRD-positivity retained statistical significance. To get insights into these issues, in the present study we investigated a large cohort of BCR-ABL1-negative B-ALL as assessed by molecular biology to evaluate: (1) the incidence and clinico-biological features of KMT2A-AFF1-positive ALL; (2) the outcome of KMT2AAFF1-positive in comparison with KMT2A-AFF1-negative ALL patients; (3) the clinico-biological parameters that affect KMT2AAFF1-positive patients' prognosis. Between November 1996 and September 2016, 926 BCR-ABL1-negative B-ALL patients (median age 34.3 years) were enrolled in the GIMEMA clinical trials LAL0496 (n = 187), LAL2000 (n = 267), LAL0904 (n = 210), LAL1104 (n = 76), LAL1308 (n = 53), LAL1913 (n = 133) (Figure S1, Table S1) with a median follow-up of 25.4 months (range: 0.1–146.9). The clinicobiological features of the cohort of study are summarized in Table S2. Overall, 97/926 (10.5%) samples harbored the KMT2A-AFF1 fusion gene, detected by RT-PCR. Molecular biology methods and statistical analyses details are described in supplemental material. The analysis of clinico-biological features at diagnosis revealed that KMT2A-AFF1-positive patients had a significantly higher median age (42 vs 32.5 years old, p < 0.001), were more likely to be female (60/97 vs 364/829, p = 0.001) and had a significantly higher median WBC count (70.7 vs 7.2 10/L, p < 0.001) than KMT2A-AFF1negative patients (Table S2). Next, we compared their outcomes. Firstly, the complete remission (CR) rate did not differ between KMT2A-AFF1-positive and -negative patients (87.5% vs 81.5%, p = 0.188). The MRD evaluation after induction treatment was available for 197 patients (26 KMT2A-AFF1-positive and 171 KMT2A-AFF1-negative) enrolled in the most recent protocols (LAL0904, LAL1308, LAL1913, LAL1104) (Table S1, Figure S1). MRD was assessed by QRT-PCR in KMT2A-AFF1-positive as detailed in supplemental material. With the caveat that the number of patients evaluated for MRD was small, KMT2A-AFF1-positive and negative patients did not differ in the achievement of MRD-negativity: indeed, 18/26 (69.2%) KMT2AReceived: 2 April 2021 Revised: 19 May 2021 Accepted: 20 May 2021