Changes in free and free-to-total prostate specific antigen after androgen deprivation or chemotherapy in patients with advanced prostate cancer.

ABSTRACT

PURPOSE: To provide preliminary data on whether the diagnostic role of serum prostate specific antigen (PSA) in assessing the response to treatment is improved by concomitant free PSA evaluation both markers were evaluated in 42 patients with advanced prostate cancer who received hormonal therapy and 57 with hormone refractory disease who received chemotherapy. MATERIALS AND METHODS: PSA was assessed at baseline and every 3 months during treatment. Free PSA was assessed in stored serum samples obtained at baseline and at maximum PSA decrease. Free PSA was not measurable in 17 patients who received androgen deprivation (40.5%) and 2 who received chemotherapy (3.5%) because it was less than 1.5 ng./ml. RESULTS: Of the 21 patients with greater than 50% PSA decrease after hormonal therapy free-to-total PSA increased in 12 (57.2%) and decreased in 9 (42.9%). Of the 20 patients with PSA response after chemotherapy free-to-total PSA increased in 18 (90.0%) and decreased in 2 (10.0%). Free-to-total PSA increased in 12 of the 20 patients (60.0%) with PSA stabilization after chemotherapy. Patients with an increase in free-to-total PSA after chemotherapy had greater survival compared to those with a decrease or no change (19.8 versus 15.5 months, respectively, p <0.03). CONCLUSIONS: These data suggest that an effective cytotoxic regimen mainly affects the protein bound PSA fraction. The absence of a clear predominant pattern of free-to-total PSA in patients with PSA response to hormonal therapy and the high percentage of hormone sensitive patients in whom free PSA was not assessable at maximum PSA decrease suggest that free PSA evaluation is less useful in prostate cancer patients undergoing androgen deprivation.