Steroid receptors and response of endometrial cancer to hormones in vitro.

The sensitivity to medroxyprogesterone acetate (MPA) and tamoxifen (T) and their combination was assayed in 13 patients with untreated endometrial cancer by an in vitro ATP-bioluminescence method. The method measures the levels of adenosinetriphosphate (ATP), the basic energy source of living cells. A tumor was considered to respond to the drug, if the proportion of living cells after manipulation was 50% or less from unmanipulated control culture. Estrogen (ER) and progesterone (PR) receptors were assayed by the DCC-method and the results calculated by Scatchard-analysis. ER (greater than or equal to 3 fmol/kg cytosol protein) was present in all tumors and PR (greater than or equal to 10 fmol/kg cytosol protein) in 85% of the tumors. The response rate in vitro to MPA was 67% (8 out of 12 tumors), to T 18% (2 out of 11) and to their combination 69% (9 out of 13). The G1 tumors responded statistically significantly better to MPA (p less than 0.01) and MPA + T (p less than 0.02) as compared to T. MPA produced higher cell kill of G1 than G2 tumors (p less than 0.05). The ER content correlated with the effect of MPA in vitro in 67%, with the effect of T in 18% and with that of their combination in 69% of the tumors. The PR content correlated with the effects of MPA in vitro in 83%, with the effect of T in 36% and with that of their combination in 54% of the tumors. It was concluded that the in vitro ATP-bioluminescence method provides valuable information besides steroid receptor determinations for sensitivity testing of endometrial cancer to hormones.