PROSTATE-CANCER VOLUME ADDS SIGNIFICANTLY TO PROSTATE-SPECIFIC ANTIGEN IN THE PREDICTION OF EARLY BIOCHEMICAL FAILURE AFTER EXTERNAL-BEAM RADIATION-THERAPY

Purpose: A new clinical pretreatment quantity that closely approximate s the true prostate cancer volume is defined. Methods and Materials: T he cancer-specific prostate-specific antigen (PSA), PSA density, prost ate cancer volume (V (Ca)), and the volume fraction of the gland invol ved with carcinoma (V (Ca)fx) were calculated for 227 prostate cancer patients managed definitively with external beam radiation therapy. 1. PSA density = PSA/ultrasound prostate gland volume 2. Cancer-specific PSA = PSA - [PSA from benign epithelial tissue] 3. V-Ca = Cancer-spec ific PSA/[PSA in serum per cm(3) of cancer] 4. V(Ca)fx = V-Ca/ultrasou nd prostate gland volume A Cox multiple regression analysis was used t o-test whether any of these clinical pretreatment parameters added sig nificantly to PSA in predicting early postradiation PSA failure. Resul ts: The prostate cancer volume (p = 0.039) and the volume fraction of the gland involved by carcinoma (p = 0.035) significantly added to the PSA in predicting postradiation PSA failure, Conversely, the PSA dens ity and the cancer-specific PSA did not add significantly (p > 0.05) t o PSA in predicting postradiation PSA failure, The 20-month actuarial PSA failure-free rates for patients with calculated tumor volumes of l ess than or equal to 0.5 cm(3), 0.5-4.0 cm(3), and >4.0 cm(3) were 92, 80, and 47%, respectively (p = 0.00004). Conclusion: The volume of pr ostate cancer (V (Ca)) and the resulting volume fraction of cancer bot h added significantly to PSA in their ability to predict for early pos tradiation PSA failure. These new parameters may be used to select pat ients in prospective randomized trials that examine the efficacy of co mbining radiation and androgen ablative therapy in patients with clini cally localized disease, who are at high risk for early postradiation PSA failure.