NOTCH1 pathway activating mutations and clonal evolution in pediatric T-cell acute lymphoblastic leukemia

Abstract

Molecular mechanisms involved in the relapse of T-cell acute lymphoblastic leukemia (T-ALL) are not fully understood, although activating NOTCH1 signaling due to NOTCH1/FBXW7 alterations is a major oncogenic driver. To unravel the relevance of NOTCH1/FBXW7 mutations associated with relapse, we performed whole–exome sequencing in 30 pediatric T-ALL cases, among which 11 diagnosis-relapse paired cases were further investigated to track the clonal evolution of relapse using amplicon–based deep sequencing. NOTCH1/FBXW7 alterations were detected in 73.3% (diagnosis) and 72.7% (relapse) of cases. Single nucleotide variations in the heterodimerization domain were the most frequent (40.0%) at diagnosis, whereas proline, glutamic acid, serine, threonine–rich (PEST) domain alterations were the most frequent at relapse (54.5%). Comparison between non–relapsed and relapsed cases at diagnosis showed a predominance of PEST alterations in relapsed cases (P =.045), although we failed to validate this in the TARGET cohort. Based on the clonal analysis of diagnosis-relapse samples, we identified NOTCH1 “switching” characterized by different NOTCH1 mutations in a major clone between diagnosis and relapse samples in 2 out of 11 diagnosis-relapse paired cases analyzed. We found another NOTCH1 “switching” case in a previously reported Berlin-Frankfurt-Münster cohort (n = 13), indicating NOTCH1 importance in both the development and progression of T-ALL. Despite the limitations of having a small sample size and a non–minimal residual disease–based protocol, our results suggest that the presence of NOTCH1 mutations might contribute to the disease relapse of T-ALL.