Hormonal therapies for breast cancer: can progestogens stimulate growth?

The human breast cancer cell line, MCF-7, displays many of the properties of breast tumours in vivo and, in particular, shows similar responses to hormones. Medroxyprogesterone acetate significantly inhibited cell proliferation, but, following continued treatment, this effect was lost and further exposure to the drug stimulated cell proliferation and increased polyamine content while tamoxifen inhibited growth. Prolonged administration of progestogens may thus have adverse effects and should be assessed critically.