The influence of prostate volume on the ratio of free to total prostate specific antigen in serum of patients with prostate carcinoma and benign prostate hyperplasia

BACKGROUND Determining the ratio of free to total prostate specific antigen (f‐PSA to t‐PSA, calculated as the percentage of f‐PSA [f‐PSA%]) in serum allows for a clearer distinction between patients with prostate carcinoma (PCa) and patients with benign prostate hyperplasia (BPH) than determining the level of t‐PSA alone. To find influencing factors on f‐PSA%, the authors investigated prostate volume, TNM classification, and tumor stage. METHODS The authors measured f‐PSA and t‐PSA in 36 men with untreated PCa (tumor classification: T1, 2, 3pN0, M0), 44 patients with BPH, and 54 healthy controls. Prostate volume was determined by transrectal ultrasound. RESULTS The median values of t‐PSA and f‐PSA% were 7.8 μg/L and 10.5% in PCa patients, 4.3 μg/L and 20.8% in patients with BPH, and 1.4 μg/L and 23.6% in the control group. Patients with PCa had a significantly lower proportion of f‐PSA than BPH patients and healthy men. There was no correlation of f‐PSA% to TNM stage or tumor grade. In PCa patients a significant positive correlation (correlation coefficient [r] = 0.51, P < 0.001) was found between f‐PSA% and prostate volume, whereas there was no significant correlation in BPH patients (r = ‐0.27, P > 0.05). There was a significant difference in f‐PSA% between PCa and BPH patients with prostate volumes smaller than 40 cm 3 (9.0% vs. 21.6%, P < 0.01) but not between patients in these 2 groups with prostate volumes exceeding 40 cm 3 (15.1% vs. 18.2%, P = 0.11). CONCLUSIONS Determining the ratio of f‐PSA to t‐PSA to discriminate between PCa and BPH patients yields significant results only in men with a prostate volume of less than 40 cm 3 . Cancer 1997; 79:104‐9. © 1997 American Cancer Society.