A prior National Cancer Institute (NCI) study (referred to as MAVE) tried to improve response rates by using a combined modality approach with chemotherapy and surgery. Prior in vitro studies had shown that mitotane inhibited Pgp and that continuous exposure to doxorubicin and vincristine was more effective at overcoming Pgp-mediated resistance than the same drugs given on an intermittent schedule. The MAVE study used daily oral mitotane with infusional doxorubicin, vincristine, and etoposide prior to tumor resection in patients with resectable or potentially resectable tumors. The results showed an overall response rate of 19% (including minor responses), and an overall median survival of 13.5 months. These results were similar to those reported with previous regimens in adrenocortical cancer (ACC). A possible explanation for the failure to achieve a higher response rate may be that mitotane was unable to inhibit Pgp. Although the serum levels of mitotane achieved in patients had been shown to block Pgp in vitro, inhibition of Pgp in patients was not accomplished, as documented by a validated surrogate assay using Pgp-expressing CD56+ cells and the Pgp substrate, rhodamine. Thus the question of whether Pgp inhibition would improve response rates remains unanswered.