Although some studies reported a lack of any possible association between ABCG2 c.421C>A and imatinib Ctrough [16,30], taken together, ours and previous reports suggest that the ABCG2 c.421C>A genotype might play a key role in modulating imatinib disposition in GIST and CML. The gene discussed is ABCG2; the disease is chronic myelogenous leukemia, BCR-ABL1 positive.