ABCB1 and gastrointestinal stromal tumor: Here, we investigated the impact of the most widely studied ABCB1 c.3435C>T, c.2677G>T/A c.1236C>T, and ABCG2 c.421C>A polymorphisms on the imatinib Ctrough in a prospective cohort of 33 Caucasian GIST patients.