Chemotherapy responsiveness of human breast tumors in the 6-day subrenal capsule assay: an update.

Feasibility of utilizing the 6-day subrenal capsule (SRC) assay to screen drugs against fresh surgical explants of human tumors was confirmed by testing six clinically active chemotherapeutic agents against 141 human breast cancers. Response rates of the six drugs obtained in the assay compared favorably with clinical response rates for the same drugs as reported by Carter (5). The evaluable assay rate for breast tumors was 92% as compared to 89% for gynecologic tumors. Innate drug resistance was indicated with 16 of 57 tumors (28%) which did not respond to any of the six agents tested. Differences in responsiveness of tumors to each agent in a potential three-drug combination of either CMF or CAF suggest that the effectiveness of multiagent therapy might be enhanced if the individual agents of a potential drug combination were selected on the basis of tumor sensitivity to each of the agents in a predictive assay. Although cross-resistance between L-PAM and cytoxan was demonstrated and was statistically significant, 31% of these tumors responded individually to either one or the other agent, suggesting caution in extrapolating concomitance in activity between these two alkylators.