Effect of short-term hormone treatment on tumorigenesis in p53-null mammary epithelial transplants. The data are the sum of two identical experiments (experiments 1 and 1A). Mice treated with estradiol and progesterone had a significant decrease in tumor incidence (p < 0.05). Filled circles, untreated; open circles, hormone-treated. The flow diagram illustrates the experimental treatment plan. C, clear mammary gland; T, transplant; E, estrogen; P, progesterone.