HISTOLOGICAL CHARACTERISTICS AND IMMUNOHISTOCHEMICAL EGF STAINING OF PREGNANCYDEPENDENT MAMMARY TUMORS OF GR/A MICE

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Histological changes of the mammary tissues during the growth of pregnancy-dependent mammary tumors (PDMT) and the immunohistochemical staining of epidermal growth factor (EGF) in these mammary epithelial cells were studied in the inbred strain of GR/A mice. Mice were mated at 60-70 days of age and subjected to concurrent pregnancy. Mice developing PDMT at the first pregnancy always retained the microscopically detectable tumors during the subsequent inter- or early pregnancy when no gorss PDMT existed. EGF staining was observed in the epithelial cells of the lactating mammary glands showing marked proliferation, but not in PDMT. These findings demonstrate that in GR/A mice PDMT repeat growth and regression, but not the complete extinction, during the reproduction and suggest that the contribution of EGF to the growth of PDMT is rather minor.