Progestin effects on growth in the human breast cancer cell line T-47D--possible therapeutic implications

In order to determine growth effects of the progestin R5020, (promegestone), we have utilized the progesterone-receptor rich human breast cancer cell line T-47D, growing the cells in the absence of the pH indicator phenol red, which has recently been found to be estrogenic. In contrast to reports on cells grown in the presence of phenol red, we find that promegestone alone, at physiological progestin concentration, significantly stimulates growth. Estradiol alone, at physiological concentration, stimulates growth much more. Promegestone in combination with estradiol is antiestrogenic for growth; that is, it significantly decreases the growth stimulatory effect of estradiol. These results raise the possibility that estrogen receptor and progesterone receptor-rich breast cancer patients might benefit more from a combination of anti-progestin and anti-estrogen therapy than from anti-estrogens alone.