Subrenal capsule assay in human breast cancer. Response to cytostatic drug combinations and correlation with receptor status.

The subrenal capsule assay (SRCA) was used to study the sensitivity of breast cancer to cytostatic drug combinations. The results were compared with steroid receptor status. Forty-five of 46 SRCAs (98%) were macroscopically evaluable. However, a histological study implied that the transplants should also be evaluated histologically, because in only 14/21 (67%) of the control SRCAs examined were histologically viable tumor cells seen. An inflammatory cell reaction was noticed in half of the cases. In the groups treated with cytostatics only 3/21 (14%) had vital tumor cells, whereas inflammation was evident in 4/21 (19%) of the cases. The rate of resistance to A + CTX was 30%. By testing several drug combinations against each tumor the rate of chemoresistance was reduced to 10%. The differences between A + CTX and the best combination were statistically significant (P less than 0.05). Of the tumors 79% were ER-positive and 67% PR-positive. Receptor-negative tumors tended to be more sensitive to cytostatics than receptor-positive tumors (100 vs 85%). The difference was not, however, statistically significant. It can be concluded that the SRCA under standardized conditions is a good method for studying the response of individual breast cancers to chemotherapy.