ABCB1 and gastrointestinal stromal tumor: In the present study, we investigated the association between ABCB1 c.3435C>T, c.2677G>T/A, c.1236C>T, ABCG2 c.421A>C, and the imatinib plasma trough concentration (Ctrough) in a prospective cohort of 33 GIST patients enrolled within a clinical trial at our Cancer Institute.