Abstract: A method is disclosed for predicting response of a tumor patient to therapy, and selecting appropriate therapy for malignant neoplasms such as breast, ovarian and gastrointestinal cancer. A sample of tumor cells is cultured in the presence of 10 .mu.g/ml estradiol, and inhibition of cell growth in the culture paradoxically indicates an estrogen dependent tumor that will respond to antiestrogenic therapy. Another sample of tumor cells is cultured in the presence of a chemotherapeutic agent which predicts response of the tumor to in vivo administration of a cytotoxic agent. The chemotherapeutic agent is preferably a cytotoxic drug, or a drug having both cytotoxic and antiestrogenic mechanisms of action. A particularly suitable substance having both mechanisms of action is: ##STR1## wherein R.sup.1 H, OH, OOC(CH.sub.2).sub.2 CO.sub.2 H or CH.sub.3 COO; R.sup.2 is C.sub.6 H.sub.4 OH, C.sub.6 H.sub.4 OCOCH.sub.3, C.sub.6 H.sub.4 OOC(CH.sub.2)CO.sub.2 H, or C.sub.6 H.sub.5 ; and X is C.sub.6 H.sub.3 -2,4(NO.sub.2).