However, the present findings, together with previous studies reporting low-level mutation frequencies of NOTCH1 and relapses of NOTCH1-positive T-ALL being negative for the mutation, as also seen in our case 47 (Additional file 4: Table S4) [39,40], show that NOTCH1 mutations also can be secondary events. This evidence concerns the gene NOTCH1 and acute lymphoblastic leukemia.