Estrogen and progesterone binding sites in renal cell carcinoma

Twenty-five renal cell carcinomas were assayed for estrogen and progesterone receptor levels. Estrogen specific binding was present in only 4 patients (16%) and progesterone specific binding in 7 patients (28%). In all cases these receptors were present in very low titers, less than 10 fm/mg. We believe that earlier reports citing significant estrogen and progesterone binding activity may reflect high levels of nonspecific protein binding.