Antiprolactinemic approach in the treatment of metastatic breast cancer: a phase II study of polyneuroendocrine therapy with LHRH-analogue, tamoxifen and the long-acting antiprolactinemic drug cabergoline.

Despite the well-demonstrated stimulatory role of prolactin (PRL) on breast cancer cell growth and the possible existence of a PRL-dependency in estrogen-independent mammary tumors, the therapeutic role of the antiprolactinemic drugs in the treatment of human breast cancer has still to be investigated and defined. Previous preliminary studies have already shown that the concomitant administration of antiprolactinemic agents may enhance the efficacy of cancer chemotherapy for breast carcinoma, whereas their impact on the efficacy of the endocrine therapy is still unknown. At present, the classic endocrine therapy for breast cancer consists of anti-estrogens plus LHRH-analogue. The concomitant administration of antiprolactinemic drugs could enhance the efficacy of treatment by blocking not only the action of estrogens, but also that of another growth factor for breast cancer, such as PRL. The present phase II study was performed to evaluate the efficacy and tolerability of a polyneuroendocrine approach for breast cancer, consisting of LHRH-analogue plus the anti-estrogen tamoxifen plus a long-acting antiprolactinemic agent, cabergoline. The study included 14 consecutive metastatic breast cancer women, heavily pretreated with the standard anticancer therapies and for whom no other conventional treatment was available. The LHRH-analogue, triptorelin, was given intramuscularly at a dose of 3.75 mg every 28 days, tamoxifen was given orally at 20 mg/day and cabergoline was given orally at 0.5 mg once/week. The clinical response consisted of partial response (PR) in 4 out of 14 (29%) patients, including one who had progressed on a previous treatment with triptorelin plus tamoxifen alone. A stable disease (SD) was achieved in another 5 patients, whereas the other 5 patients had a progressive disease (PD). Mean serum levels of PRL significantly decreased on treatment within the first month of therapy, and its decline was significantly more evident in patients with PR or SD than in those with PD. The treatment was well-tolerated in all patients, and in particular no cabergoline-related toxicity occurred. This preliminary study would suggest that the association of the long-acting antiprolactinemic drug cabergoline may further enhance the efficacy of the classical endocrine therapy for advanced breast cancer with anti-estrogens plus LHRH-analogues.