Figure 1.

Progestins inhibit the estrogen-dependent growth of ER+PR+ breast cancer PDX. A, Tumors UCD4 and UCD65 were grown in mice supplemented with continuous E2, E2+P4, or E2+MPA. Sections were stained by IHC for ER, PR, and AR under each of the conditions as indicated. Scale bars, 200 um. Scale bars for insets, 60 um. Quantitation of IHC is in Supplementary Fig. S1A. B and C, Tumors were grown in mice either in the absence of exogenously added hormones (placebo), or in the presence of continuous E2, E2+P4, or E2+MPA. Tumor volumes were measured weekly and plotted versus the number of days of incubation ± SEM. Tumor volumes at the final time point were compared using ANOVA followed by a Tukey post-hoc multiple comparison test. Significance (P values) is indicated. n=6–8 tumors per condition. Experiments were performed a minimum of two times with the same statistically significant results. D, UCD4 tumors were grown in mice supplemented with E2 until they reached an average volume of 300 mm³, then either implanted with an MPA pellet, or treated 3 times weekly with tamoxifen (E2+TAM) or vehicle (E2+Veh). Tumor volumes at the final time point were compared using one-way ANOVA followed by a Tukey post-hoc multiple comparison test. n=6 tumors per condition. Significance is indicated; bars represent mean ± SEM.