Expression of ER and P21 Ras Protein in N-Nitrosomethylurea-Induced Rat Mammary Tumors. Preliminary Report.

ˆ The study of the expression of estrogen receptor (ER) during mammary carcinogenesis should allow a better understanding of the sequential steps of the natural history of human breast cancer. To verify this hypothesis chemical induced mammary tumors were exploited. The N-nitrosomethy1 urea (NMU) induced rat mammary tumor, is the best mode for human breast cancer, set up by Gullino 1 . The NMU induces a high yield of mammary carcinomas in 73% of Sprague-Dawley rats, with a latent period of 86 days. These tumors have estrogen (E), progesteron (Pg), prolactin (PRL) and glucocorticoids (G) receptors (R) 2, 3 and regress after ovariectomy 2 , administration of tamoxifen 4 or LHRH analogs 5 . Recently, the activation of the locus Ha-ras 1 was demonstrated in rat mammary tumors raised by a single treatment with NMU 6 .