Stimulation of mammary carcinoma cell proliferation by epithelial growth factor in vitro.

Mammary carcinogenesis in the C3H mouse involves a complex interaction of viral, genetic, and hormonal factors, and this experimental model for breast cancer has been the subject of extensive investigation. Hormonal factors may be important both in the neoplastic transformation (6) and in the regulation of the rate of tumor growth (9). Previous studies demonstrated that cell proliferation in C3H mammary carcinoma expiants is stimulated by the addition of insulin to the synthetic medium, and the rate at which cells enter the DNA-synthetic (S) phase of the cell cycle may be further modified by estrogenic hormones (9). A protein has been isolated from the submaxillary salivary glands of mice which stimulates growth of epidermal cells (2). Under appropriate conditions the purified epidermal growth factor (EGF) causes increased numbers of epidermal cells to synthesize DNA (3). It may stimulate several types of rat epithelial cells to proliferate and has consequently been termed the "epithelial growth factor" (4). Although the