G Representative micrographs of PR-IHC on glands from 5-month-old MM134 xenografts from hosts treated for 2 months with vehicle (left) or E2 (right) pellets. Scale bars, 200 μm. Right, bar plot showing percentage of PR+ cells in MM134 and SUM44 xenografts with n>1000 cells per condition on glands from 3 different mice. Data represent mean ± SEM unpaired, Student's t-test, two-tailed; *** p < 0.001, **** p < 0.0001. 