The combined effect of nonsteroidal anti-oestrogens and sex steroids on the growth of rat uterine adenocarcinoma cells in tissue culture.

Nonsteroidal anti-oestrogenic drugs, tamoxifen and clomiphene citrate, at concentrations higher than 0.001 mug/ml reduced the colony forming ability of cells derived from a rat uterine adenocarcinoma in vitro. The 50 per cent inhibitory dose of these drugs was about one-hundredth of that of sex steroids. When the cells were treated with combinations of these nonsteroidal anti-oestrogenic drugs and the 50 per cent inhibitory dose (8 mug/ml) of progesterone, a synergistic effect on the inhibition of colony formation was observed. In contrast to progesterone, oestradiol-17beta (the 50 per cent inhibitory dose of which was about 16 mug/ml) suppressed additively the colony formation only in combination with low doses of anti-oestrogenic drugs.