Determination of estrogen receptors in canine mammary tumors.

Dextran-coated charcoal assay with Scatchard plotting was used for the quantitative determination of high-affinity estradiol receptors (ER) in 10 canine mammary tumor cytosols. Mammary tumors diagnosed histopathologically as adenocarcinomas appeared to have a higher incidence of ER than those diagnosed as mixed mammary tumors. These receptors have a high affinity for estradiol with dissociation constants as determined by Scatchard analysis ranging from 1.2 to 2.0 X 10(-11) M. These dissociation constants are similar to those previously reported for the receptor-estradio interaction from target tissues in other species. The specific binding of the receptor for the hormone was diminished in the presence of an antiestrogenic compound. Our data suggest that canine mammary tumors with significant ER levels would respond favorably to antiestrogen therapy. With the demonstration of ER sites in canine mammary adenocarcinomas as presented herein, the potential for chemotherapeutic management appears to be encouraging.