Imatinib was the first signal transduction inhibitor (STI) used in a clinical setting and it functions by preventing a breakpoint cluster region (BCR)-abelson murine leukemia viral oncogene homolog fusion (BCR-ABL fusion) protein from exerting its role in the oncogenic pathway in CML [53,54,55]. Here, BCR is linked to chronic myelogenous leukemia, BCR-ABL1 positive.