The protective effects of E+P treatment are not retained in epithelial transplant outgrowths. (a) Donor tissues were obtained from Trp53+/- mice that were treated as summarized in the diagram. One group of mice was implanted with pellets containing either no hormones or E+P. Another group of mice was allowed to undergo a full-term pregnancy or remained unmated to provide age-matched nulliparous tissue. (b) Radiation-induced apoptosis was determined in outgrowths of Trp53+/- mammary tissue transplanted into wild-type hosts. The timeline of treatments is summarized graphically in the upper panel. The Trp53+/- mammary tissues from donors, described in panel (a), were transplanted into mammary fat pads of 3-week-old wild-type hosts and allowed to fill the glands. When 10 weeks old, the transplant-bearing hosts were irradiated 6 hours prior to tissue harvest. Radiation-induced apoptosis was low and did not differ among the mammary epithelial outgrowths from Trp53+/- placebo-treated, E+P-treated, age-matched virgin (AMV), or parous mammary tissues. E+P, estradiol and progesterone; Trp53, transformation-related protein 53 (gene in mouse encoding the p53 tumor suppressor protein); TUNEL, terminal uridine deoxynucleotidyl transferase dUTP nick-end labeling.