el-Shirbiny A M
Nuclear Medicine Department, Albert Einstein Medical School, NY, NY 10461.
Adv Clin Chem. 1994;31:99-133. doi: 10.1016/s0065-2423(08)60334-0.
PSA is a 34-kDa 240-amino-acid glycoprotein produced exclusively by prostatic epithelial cells. PSA is a serine protease, is a member of the kallikrein gene family, and has a high sequence homology with human glandular kallikrein. It has chymotrypsin-, trypsin-, and esterase-like activities. In the serum it is present mainly in a complex form with alpha 1-antichymotrypsin. It is secreted in the seminal plasma and is responsible for liquefaction of the seminal coagulum. The production of PSA proteins appears to be under the control of circulating androgens acting through the androgen receptors. The PSA gene is up-regulated predominantly by androgens at both the protein and mRNA levels. DRE causes minimal changes in the PSA level, while prostate massage, ultrasonography, systoscopic examination, and prostate biopsy can all cause clinically significant elevations. Other conditions, such as prostatitis, prostate intraepithelial neoplasia, acute urinary retention, and renal failure can also elevate the PSA level. The value of PSA as a screening tool is questionable because of the great deal of overlap in PSA levels between BPH and prostate cancer. However, if used in men over 50, in conjunction with DRE and/or ultrasonography, it may become a vital part of the early detection program. PSA's role in determining the clinical and pathological stage is also limited, in spite of the direct correlation between the pathological stage and the PSA level, because of great overlap in the PSA levels in various stages. The most important clinical utility of PSA is in monitoring patients after definitive therapy. PSA is most sensitive and reliable in the detection of a residual tumor, possibly recurrence, or disease progression following treatment, irrespective of the treatment modality. PSA can accurately predict the tumor status and can detect recurrence several months before its detection by any other method. PSA is also a very sensitive and specific immunohistochemical marker for tumors of prostatic origin. Compared to PAP, PSA is a more precise and meaningful marker in all clinical situations. With the development of ultrasensitive assays and the adoption of an international standard PSA calibrator, so that results from multicenter studies can be compared, PSA could become one of the most useful tumor marker in cancer biology.
前列腺特异性抗原（PSA）是一种由前列腺上皮细胞专门产生的34千道尔顿、含240个氨基酸的糖蛋白。PSA是一种丝氨酸蛋白酶，属于激肽释放酶基因家族成员，与人类腺体激肽释放酶具有高度的序列同源性。它具有胰凝乳蛋白酶、胰蛋白酶和酯酶样活性。在血清中，它主要以与α1 -抗胰凝乳蛋白酶结合的形式存在。它分泌到精浆中，负责精液凝块的液化。PSA蛋白的产生似乎受通过雄激素受体起作用的循环雄激素的控制。PSA基因在蛋白质和mRNA水平上主要由雄激素上调。直肠指检（DRE）对PSA水平的影响极小，而前列腺按摩、超声检查、膀胱镜检查和前列腺活检都可能导致临床上显著的升高。其他情况，如前列腺炎、前列腺上皮内瘤变、急性尿潴留和肾衰竭也可使PSA水平升高。由于良性前列腺增生（BPH）和前列腺癌之间的PSA水平有大量重叠，PSA作为一种筛查工具的价值存在疑问。然而，如果用于50岁以上男性，并结合DRE和/或超声检查，它可能成为早期检测计划的重要组成部分。尽管病理分期与PSA水平直接相关，但由于不同分期的PSA水平有很大重叠，PSA在确定临床和病理分期中的作用也有限。PSA最重要的临床用途是在确定性治疗后监测患者。无论治疗方式如何，PSA在检测残留肿瘤、可能的复发或治疗后疾病进展方面最为敏感和可靠。PSA可以准确预测肿瘤状态，并能在通过任何其他方法检测到复发前数月就检测到。PSA也是前列腺源性肿瘤非常敏感和特异的免疫组化标志物。与前列腺酸性磷酸酶（PAP）相比，在所有临床情况下，PSA都是更精确和有意义的标志物。随着超灵敏检测方法的发展以及国际标准PSA校准物的采用，以便多中心研究的结果能够进行比较，PSA可能成为癌症生物学中最有用的肿瘤标志物之一。
