Presentation of a functional pituitary adenoma as a significant decrease in prostate-specific antigen level in a patient followed for prostate cancer.

The stimulatory role of testosterone in the production and release of prostate-specific antigen (PSA) has been well characterized. Testosterone production by the testes is dependent on a functional hypothalamic-pituitary-gonadal axis. High prolactin levels have been shown to disrupt this axis, resulting in decreases in gonadotropins and testosterone levels. We report a patient with prostate cancer and elevated PSA levels followed with "watchful waiting" for several years who experienced a precipitous decrease in PSA level over a 3 month period. The patient was found to have an asymptomatic prolactin-secreting pituitary macroadenoma.