Effect of bicalutamide therapy on prolactin response to L-dopa in metastatic prostate cancer patients.

OBJECTIVES: The secretion of prolactin (PRL), which is a growth factor for prostate cancer cell proliferation, has been proven to present profound alterations in advanced prostate cancer patients, consisting of abnormally elevated baseline levels and paradoxical response to L-dopa. Moreover, the efficacy of standard therapies for prostate cancer may be mediated at least in part by changes in PRL secretion. The present study was carried out to analyze the effects of the new antiandrogen agent bicalutamide on basal levels of PRL and on its response to L-dopa in metastatic prostate cancer patients.

MATERIAL & METHODS: The study included 10 metastatic prostate cancer patients. They were treated with bicalutamide at a dose of 50 mg/day orally. They were investigated with L-dopa test before therapy and after one month of treatment. L-dopa was given orally at 500 mg, by collecting blood samples before and at 60, 120 and 180 minutes after L-dopa administration. Serum levels of PRL were measured by the RIA method.

RESULTS: Abnormally basal levels of PRL were seen in 4/10 (40%) patients. Mean PRL basal levels decreased after bicalutamide therapy, without, however, significant differences. Before therapy, a paradoxical increase in PRL levels after L-dopa occurred in 4 patients, 3 of them showed basal concentrations of PRL within the normal range. Moreover, bicalutamide therapy significantly reduced PRL increase in response to L-dopa.

CONCLUSIONS: This study would suggest that the measurement of the only basal levels is not sufficient to define as normal the secretion of PRL in advanced prostate cancer, because of the possible existence of altered response to the dynamic tests for PRL secretion. Moreover, the study shows that the antitumor therapy with the new anti-androgen bicalutamide may reduce PRL secretion and improve its paradoxical secretion in response to L.-Dopa. Further studies will be required to better define the possible prognostic impact of changes in PRL secretion on the efficacy of treatments for metastatic prostate cancer.