STEROID-RECEPTORS IN MAMMARY-TUMORS OF THE CAT

The capacity of steroidal regulatory influence on benign and malignant mammary tissue in cats was investigated. Estrogen, progestin, and (in some cats) androgen receptor levels in the cytosol were measured by a multiconcentration dextran-coated charcoal method in non-affected mammary tissue (NAMT) and in benign and malignant mammary lesions from 34 cats. Receptor levels < 5 fmol/mg protein were considered negative. Since 3 out of 4 NAMT semples had low-positive estrogen receptor and progestin receptor levels, we considered specimens in which tumour cells were intermeshed with NAMT separate from "pure" tumour specimens. The variation in estrogen receptor expression between the different tissues was moderate, there being 9/17 malignant lesions (without NAMT) estrogen receptor + as compared with 6/6 benign lesions (without NAMT) (p < 0.05). The variation in progestin receptor expression was greater (p < 0.02), with only 5/17 malignant lesions-(without NAMT) progestin receptor + as compared with 6/6 benign lesions (without NAMT). The difference in progestin receptor levels between these 2 groups was also statistically significant. In 5 cats metastases were also assayed and 2 had a low-positive estrogen receptor level, whereas 1 had a low-positive progestin receptor level. Two of 9 malignant lesions (without NAMT) had positive androgen receptor levels. Comparison of the steroid receptor expression of human and feline mammary cancer indicates that estrogen receptor and progestin receptor levels are lower in the latter. This may indicate that loss of steroid hormone dependency occurs at an earlier stage of the disease in feline mammary cancer than in human breast cancer. On the other hand, the low level of receptor expression in feline mammary cancer may also be due the fact that many animals are ovariectomized before manifestation of the disease.