EVALUATION OF IN-VITRO CHEMOSENSITIVITY OF ANTITUMOR DRUGS USING THE MTT ASSAY IN FRESH HUMAN BREAST-CANCER

Practical criteria were developed in this paper for the purpose of eva luating chemosensitivity of fresh human breast cancer by the MTT assay . The survival rates at maximum inhibition (Imax %) and the concentrat ions of drugs which caused fifty percent reduction in absorbance compa red to baseline values (IC50) of 175 samples of 10 anti-tumor drugs we re evaluated by logistic analyses of the dose-response curves. Distrib utions of Imax% appeared as normal curves, while those of the IC50 sig nificantly deviated from normal distribution (p < 0.0001). We assessed the in vitro chemosensitivity by comparing the Imax % of each drug on individual samples with the mean Imax % + SD which was obtained from the Imax% of 175 samples. If the individual Imax % > mean Imax % + SDI we thought the tumor sample was resistant to this drug. If the Imax % less than or equal to mean Imax % + SD, we would compare its IC50 wit h Q(50) which was used as a cutoff point for in vitro chemosensitivity of anti-tumor drugs. The in vitro chemosensitivity could be graded as sensitive (Q(1)-Q(25)), intermediate (Q(26)-Q(75)), and resistant (Q( 76)-Q(100)) by means of percentile method. If the individual IC50 grea ter than or equal to Q(76), the tumor sample would be defined as resis tant. If the individual IC50 less than or equal to Q(25), it would be defined as sensitive. In the range of Q(26)-Q(75), we used Q(50) as a cutoff point between relative sensitivity and relative resistance. Pre liminary results showed that the in vitro chemosensitivity to differen t anti-tumor drugs determined by these criteria were consistent with t he clinical response in 83 advanced breast cancer patients.