ABL1 and chronic myelogenous leukemia, BCR-ABL1 positive: Furthermore, standard diagnostic FISH analyses using commercial dual fusion probes for BCR::ABL1 (used whenever CML or ALL is suspected) may sometimes show an abnormal signal pattern for ABL1 (mostly the presence of an extra signal) but no fusion with BCR. Next generation sequencing, at both DNA and RNA level, is an effective method to screen for presence of cryptic rearrangements/fusion genes.