Secretion of transferrin by human breast cancer cells.

Transferrin (Tf), the major iron-binding protein in the plasma of vertebrate species is an essential growth factor for cells in serum-free media and appears to be involved in the regulation of growth and differentiation of human tissues. We report here that human breast cancer cells secrete a factor immunologically similar to Tf. The secretion of Tf by the hormone-responsive cell-line MCF-7 is stimulated by 17 beta-estradiol and reduced by the antiestrogen 4-hydroxy tamoxifen. These data suggest that Tf secreted by breast cancer cells may be an additional autocrine growth factor confering selective advantages to rapidly proliferating breast cancer cells and perhaps permit tumor cell growth in poorly vascularized areas.