Autoradiographic demonstration of estrogen binding in human breast cancer after in vitro incubation.

This report describes the localization of bound radioactivity as visualized by thaw-mount autoradiography in 35 cases of human breast carcinoma after in vitro incubation with [3H]estradiol. The findings have been compared qualitatively with results of biochemical assays. Twenty-six tumors were considered to be estrogen receptor positive by autoradiographic criteria. Of these, 23 were assayed biochemically; 21 were found to be positive. Specific uptake of radioactivity was observed primarily in neoplastic epithelial cells. The grains were localized mainly over the nuclear region of putative target cells. Within nests of infiltrating carcinoma, positive cells could be identified admixed with negative cells. There were no autoradiographic criteria established for borderline cases. The remaining nine cases were considered negative. In these cases the appearance of tissue exposed only to [3H]estradiol resembled that of tissue incubated with excess unlabeled estradiol. The few grains were randomly scattered with no evidence of nuclear localization. Of these negative cases, two were positive by biochemical assay, four borderline, and three negative. It is concluded that, as assessed in this investigation, estrogen receptor-positive mammary carcinomas may be composed of target and nontarget neoplastic cells. Thaw-mount autoradiography should prove useful in the laboratory investigation of steroid hormone responsiveness of human breast carcinoma.