Pretherapeutic cytostatic agent sensitivity testing of breast cancer.

With and without addition of cytostatic agents, incorporation of radiolabeled precursors into the nucleic acid of breast cancer cells was determined in short-term culture. The labeling index, a measure of tumor proliferation, depended largely on cytologic differentiation. Incorporation of radiolabeled precursors in moderately and low differentiated breast cancers was significantly high, whereas only in a part of these tumors was incorporation inhibited by adriamycin and cyclophosphamide. Therefore a group of drug sensitive and metabolic drug resistant tumors could be defined in vitro. Primary resistance against the tested cytostatic agents has been proved in low proliferating and high differentiated breast cancer cells.