: OBJECTIVE: Hyperprolactinemia is a frequent evidence occurring in both metastatic breast cancer and prostate cancer, and it has been proven to be associated with poor prognosis and reduced efficacy of the anticancer therapies. Therefore, the pharmacological control of cancer-related hyperprolactinemia could improve the prognosis of advanced breast and prostate carcinomas. Unfortunately, at present it is still controversial which may be the treatment of cancer-related hyperprolactinemia, which could depend at least in part on a direct autocrine production by cancer cells themselves. The present study was performed to evaluate the acute effects of the long-acting dopaminergic agonist bromocriptine on cancer-related hyperprolactinemia. METHODS: The study included 10 women affected by metastatic breast cancer and 10 men with metastatic prostate cancer, showing persistent hyperprolactinemia. Venous blood samples were collected before bromocriptine, and 2, 4, 10 and 24 hours after bromocriptine administration (2.5 mg orally) serum levels of PRL were measured with the double antibody RIA method. RESULTS: Bromocriptine induced a normalization of PRL levels in both groups of patients with breast and prostate cancers. Moreover, mean levels of PRL persisted significantly lower than those found before therapy during the whole 24-hour circadian period. DISCUSSION: This preliminary study shows that low-dose bromocriptine is sufficient to acutely normalize PRL secretion in both metastatic breast cancer and prostate carcinoma patients, irrespectively of the mechanisms involved in inducing cancer-related hyperprolactinemia. Therefore, low-dose bromocriptine could be recommended in association with the classical antitumor therapies in the treatment of metastatic breast cancer and prostate carcinoma patients showing cancer-related hyperprolactinemia, in an attempt to improve the efficacy of anticancer therapies themselves.