[In vitro resistance testing of tumors in relation to cytostatics. 2. Examinations with human malignomas].

The in vitro test presented here can be used to demonstrate chemotherapy drug (CD) resistance in human tumors showing high metabolic activity. Initially, dose-effect ratios are determined for various CDs in patients showing in vivo CD resistance (primary or secondary) and correlated with the inhibition of incorporation rates for radiolabeled DNA and RNA precursors in tumor cells. The maximal incorporation inhibition noted was 28% for the highest CD concentration used, and 17% for one tenth of that concentration, compared to controls. Accordingly, those tumor cells were termed "resistant" which showed a maximal incorporation inhibition of 28 and 17%, respectively, under the highest CD concentration used for the test. A total of 94 human tumors were tested, and the patient's response to CDs was evaluated after 12 weeks of therapy. In 57 of them, the in vitro test correctly predicted CD resistance as confirmed by the clinical course. There was no resistance demonstrated in vitro in another 13 cases which actually showed progression of disease while receiving CDs. In 24 cases there was good agreement between lack of resistance in vitro and clinical response.