The D-FISH system is adequate for the diagnosis and therapeutic monitoring of CML with the classical t(9;22) (1G1O2F pattern) (Figure 2A, upper panel) and even for cases with ABL1 or BCR deletion, because in the latter, the single genuine fusion can be readily differentiated from random signal overlap due to the 'extra' green or orange signal (Figure 2B–C, upper panel). Here, BCR is linked to chronic myelogenous leukemia, BCR-ABL1 positive.