Transient resistance to sunitinib in vitro. To recover cells from continuous sunitinib exposure, 786-O- and HT-29– resistant cells were cultured in sunitinib-free medium for a period of up to 12 weeks. A, sensitivity of revertant cells after 4, 8, and 12 weeks of drug-free culture conditions. Cells recovering from continuous sunitinib exposure gradually regained sensitivity to the level of parental cells. B, growth rate of revertant cells after 1, 4, 8, and 12 weeks of drug-free culture conditions. PAR, parental cells; SUN, sunitinib-resistant cells; REV, revertant cells after 1 week (REV1); 4 weeks (REV4), 8 weeks (REV8), and 12 weeks (REV12) in drug-free medium. Results are shown as means ± SEM.