DISTRIBUTION OF EPIDERMAL GROWTH-FACTOR RECEPTORS IN NORMAL AND NEOPLASTIC MAMMARY TISSUES

Epidermal growth factor (EGF) is considered to be mitogenic for prolif eration of mammary glands in animals. The action of EGF is mediated by specific EGF receptors (EFG-R). In the present study, we investigated distribution of EGF receptors during various physiological stages of mammary glands, N-methyl-N-nitrosourea (MNU)-induced mammary tumors in rats and human breast cancer samples. EGF receptor concentrations wer e determined by Scatchard analyses in the membrane fraction of the tis sues. Results showed increased EGF receptor levels in the structurally differentiated mammary tissues from pregnant rats; whereas lower conc entrations were observed in the functionally differentiated glands fro m lactating rats. EGF receptors were absent in the majority of the tum ors induced by MNU. The loss of EGF receptor was not observed during t he first 20 days post carcinogen treatment, but appeared to be correla ted with the onset of the tumor. Consistent with the literature, the m ajority of the steroid receptor positive human breast cancer samples w ere EGF receptor negative, whereas steroid receptor negative samples c ontained EGF receptors. These results suggest that the loss of EGF rec eptors in ovarian hormone dependent mammary tumors does not occur grad ually during carcinogenesis but appears to be a characteristic of horm one dependent mammary tumor cells.