Prognostic significance of serum prolactin levels in advanced breast cancer.

Serum prolactin concentrations were measured in 135 postmenopausal patients with advanced breast cancer prior to their treatment with one of 3 endocrine therapies: aminoglutethimide (AG), tamoxifen (T) + AG, or T + AG + danazol. The mean level of prolactin was higher, and there were more individuals with levels of prolactin greater than or equal to 500 mIUl-1, in the group of patients who did not respond to treatment. Of the patients whose disease progressed, those with prolactin levels greater than or equal to 500 mIUl-1 had a significantly shorter survival. It appears that high prolactin levels indicate a poor prognosis to endocrine therapy and the probability of a shorter than average survival time.