Chemically induced rat mammary tumor treated with tamoxifen showed decreased expression of cyclin D1, cyclin E, and p21(Cip1)

We studied the effects of tamoxifen (TAM) on the growth of 7,12-dimethylben z(a)anthracene (DMBA)-induced rat mammary tumor and the expression of cycli n DI, cyclin E, p21(Cip1), and estrogen receptors (ER) by performing immuno histochemistry and Western blot analysis. When tumor size reached between 1 0 and 15 nim. in the largest dimension, the rats were divided into a DMBA-c ontrol group and a DMBA-TAM group. The administration of TAM markedly decre ased the tumor development and showed decreased expression of bromodeoxyuri dine, cyclin D1, cyclin E, and p21(Cip1) when compared with those of the DM BA-control group; however, a few tumors showed progressive growth in spite of TAM treatment. These tumors had decreased expression of ER. This study s uggests that TAM suppresses tumor development through the down-expression o f cyclin D1 and cyclin E. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.