AB - Using a double-labeling immunocytochemical-autoradiographic assay we studied 18 male breast carcinomas to evaluate the cell kinetic and receptor status in neoplastic cells during S-Phase and to detect possible differences with respect to 21 female breast cancers, from a previously, published study. In male breast cancer, the tumor receptor content and ER/PgR expression in neoplastic cells during S-Phase was higher (p = ) than that in corresponding female tumor while tumoral cell proliferation was lower, but not significantly. In the previous reported study on female breast cancer we demonstrated that proliferative activity was higher in receptor negative cell population both for ER and PgR. Conversely, in male tumor, that difference was only present in relation to the expression of PgR: in fact, the proliferative activity was higher in PgR negative than in PgR positive cells (Anova Test: p = ) while no difference was evidenced between ER negative versus ER positive cells. Moreover, the arrest of DNA synthesis, expressed as percentage of cells without 3H-Tdr labeling, was not related to either the ER or PgR expression, while in female breast cancer it was higher in PgR positive than ER positive cell population. Our data confirmed differences between males and females regarding the receptor status and cell cycle S-Phase in breast cancer. The poorer prognosis of the male breast carcinoma might be related to ineffective therapies which do not consider these differences in the biological profile of the male tumor. The Authors indicate that prognostic and predictive tissutal markers, detected by immunocytochemical methods and useful for therapeutic programming in the female breast cancer have a different significance in the male breast cancer and stress the need for different therapeutic strategies specific for male breast cancer.
A receptor which is capable of producing a biological response in the absence of a bound ligand is said to display "constitutive activity".  The constitutive activity of a receptor may be blocked by an inverse agonist . The anti-obesity drugs rimonabant and taranabant are inverse agonists at the cannabinoid CB1 receptor and though they produced significant weight loss, both were withdrawn owing to a high incidence of depression and anxiety, which are believed to relate to the inhibition of the constitutive activity of the cannabinoid receptor.
Sex hormone-binding globulin (SHBG) is thought to mainly function as a transporter and reservoir for the estradiol and testosterone sex hormones. However it has also been demonstrated that SHBG can bind to a cell surface receptor (SHBG-R). The SHBG-R has not been completely characterized. A subset of steroids are able to bind to the SHBG/SHBG-R complex resulting in an activation of adenylyl cyclase and synthesis of the cAMP second messenger.  Hence the SHBG/SHBG-R complex appears to act as a transmembrane steroid receptor that is capable of transmitting signals to the interior of cells.