PROMOTER EFFECT OF MEDROXYPROGESTERONE ACETATE (MPA) IN N-METHYL-N-NITROSOUREA (MNU) INDUCED MAMMARY-TUMORS IN BALB C MICE/

The promoter effect of medroxyprogesterone acetate (MPA) on mammary ca rcinogenesis in female BALB/c mice was investigated using methylnitros ourea (MNU) as initiator. Nine out of 43 animals developed mammary car cinomas in the group treated with MNU (50 mg/kg) and MPA (administrati on of 40 mg every 3 months) starting 1 week after MNU administration. No tumors appeared in controls receiving only MNU or MPA during the ti me course of the experiment (9 months). The tumors were lobular adenoc arcinomas showing different degrees of squamous differentiation with l ow or undetectable estrogen and progesterone receptors, and expressing epidermal growth factor receptors. These results support the hypothes is that MPA promotes the growth of MNU induced lesions.