In the present study, archival fixed bone marrow chromosome suspensions from 19 CML patients and 10 CML cell lines known to carry more than 1 copy of BCR/ABL1 fusion were analyzed by fluorescent in situ hybridization (FISH) in order to investigate whether CML patients with a double Ph have two exact copies of the Ph chromosome or there are instead cryptic chromosomal rearrangements involving BCR/ABL1 fusion gene amplification as found in cell lines [9]. Here, ABL1 is linked to chronic myelogenous leukemia, BCR-ABL1 positive.