Hormone binding by human mammary carcinoma.

The specific binding of labeled porcine insulin, human prolactin, and human growth hormone was studied in 63 human breast tumors and 15 nonmalignant breast tissues. Most (90%) of the tumors demonstrated significant binding of insulin, as did 80% of nonmalignant tissues. Autoradiographic studies indicated that insulin bound dominantly to tumor cells, rather than to fat and fibrous tissue contained within tumors. Specific binding of prolactin and growth hormone of greater than 1% was seen in 20 and 12% of tumors, respectively, and one tumor studied in detail showed a small amount of saturable, high-affinity prolactin binding. The affinity of binding of insulin and prolactin to tumor was similar to that seen in target tissues in subprimate species (Kd = 4 X 10(-10) M), but the prolactin-binding capacity in the one tumor studied in detail was very low (10 fmoles/mg membrane protein), compared with prolactin-responsive experimental mammary carcinoma.