The chemosensitivities of 18 estrogen–receptor–positive (ER+) tissues were compared with that of 38 estrogen–receptor–negative (ER–) tissues, using the in vitro succinate dehydrogenase inhibition test. These human breast tissues were exposed to six antitumor drugs: carboquone, adriamycin, mitomycin C, aclacinomycin A, cisplatin and 5–fluorouracil. Decrease in succinate dehydrogenase activity was noted in ER" compared to ER+ tissues, exposed to six antitumor drugs, in particular to adriamycin (p < 0.001) and aclacinomycin A (p < 0.05). The sensitive rates were higher in ER" than in ER+ tissues, against all six antitumor drugs. The resistance rates to all drugs tested were 25% in ER" and 45% in ER+ tissues. A higher chemosensitivity is associated with the absence of ER. It appeared that the ER status in case of breast cancer is an important predictor of the response to chemotherapy.
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