Elacridar (GF120918), which is an ABCG2 and ABCB1 inhibitor, increased the oral bioavailability of topotecan from 40% to approximately 100% in randomized trials on different cancer patients (non-small cell lung cancer, small cell lung cancer, ovarian adenocarcinoma, appendix carcinoma, pancreas carcinoma, squamous cell carcinoma, bladder carcinoma, and gastric carcinoma) [112,113]. Here, ABCB1 is linked to small cell lung carcinoma.