Enhanced Expression of Prostate-Specific Antigen in the Transition Zone of the Prostate

Abstract

Objective: To determine whether the serum levels of total prostate-specific antigen (t-PSA), free PSA (f-PSA) and PSA complexed to α₁-antichymotrypsin (PSA-ACT) result from different expressions in various prostatic zones. Methods: In a series of 127 consecutive men undergoing transurethral resection of the prostate (TURP) for BPH between May 1995 and February 1996, t-PSA, f-PSA (ProStatus^™, Wallac) and PSA-ACT were measured before and 3–4 months after surgery. Pre- and postoperative prostate volumes were measured by TRUS. Resected tissue was assumed to be the transition zone (TZ) while postoperative volume was defined as peripheral zone (including the central one) (CPZ). Pre- and postoperative serum PSA was related to pre- and postoperative volume and resected tissue to the difference between pre- and postoperative serum PSA, respectively. The serum PSA per 1 g tissue was calculated. Group I consisted of 96 historically proven BPH with no signs of inflammation, group II of 19 BPH patients with transurethral catheters inserted sometime prior to surgery to relieve urinary retention, and group III of 12 patients with incidental carcinomas. Results: In patients undergoing TURP without prior catheterization (group I) t-PSA (group I) declined from median 3.43 to 0.96 ng/ml after TURP by 72%, even though the prostate volume did so only by 44%, whereas the ratio free-to-total (f/t) PSA remained stable (median 24.9% pre- vs. 26.6% postoperatively). The TZ expressed approximately 2.7-fold more t-PSA than the remaining CPZ: median 0.14 vs. 0.052 ng/ml/g, respectively, and as to f-PSA it did so likewise: median 0.032 vs. 0.012 ng/ml/g, respectively. With transurethral catheterization prior to surgery (group II) the t-PSA density within whole prostate increased 1.4-fold as compared to this density without such catheterization: from median 0.089 (group I) to 0.13 ng/ml/g tissue, respectively (p < 0.007), and within the TZ alone 1.6-fold elevation from median 0.14 to 0.23 ng/ml/g, respectively (p < 0.02) was observed. In incidental carcinoma (group III) a reduced ratio of f/t PSA of 11.7% in the TZ as compared to 22.1% in the CPZ (22.1%) was observed. Conclusions: In BPH both t-PSA and f-PSA are predominantly expressed within the TZ, which could help to improve the specificity of the PSA density in cancer detection by using the sum of the t-PSA densities of the TZ and CPZ: (0.14 ng/ml/g × TZ) + (0.052 ng/ml/g × CPZ). It is the first time that the supposed origin of the incidental carcinoma (from the TZ) is confirmed biochemically by a f/t PSA ratio exclusively reduced in the TZ but not in the CPZ. The post-TURP unchanged free-to-total ratio (26.6%) may be useful for the early detection of cancer in patients followed up after TURP.