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 approximates the true prostate cancer volume is defined. Methods and Materials: The cancer-specific prostate-specific antigen (PSA), PSA density, prostate cancer volume (V (Ca)), and the volume fraction of the gland involved 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-specific PSA/[PSA in serum per cm(3) of cancer] 4. V(Ca)fx = V-Ca/ultrasound prostate gland volume A Cox multiple regression analysis was used to-test whether any of these clinical pretreatment parameters added significantly to PSA in predicting early postradiation PSA failure. Results: 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 density and the cancer-specific PSA did not add significantly (p > 0.05) to PSA in predicting postradiation PSA failure, The 20-month actuarial PSA failure-free rates for patients with calculated tumor volumes of less 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 prostate cancer (V (Ca)) and the resulting volume fraction of cancer both added significantly to PSA in their ability to predict for early postradiation PSA failure. These new parameters may be used to select patients in prospective randomized trials that examine the efficacy of combining radiation and androgen ablative therapy in patients with clinically localized disease, who are at high risk for early postradiation PSA failure.