Zagars G K, Pollack A
Department of Radiotherapy, University of Texas, M.D. Anderson Cancer Center, Houston 77030.
Cancer. 1993 Aug 1;72(3):832-42. doi: 10.1002/1097-0142(19930801)72:3<832::aid-cncr2820720332>3.0.co;2-6.
The serum kinetics of prostate-specific antigen (PSA) after radiation therapy for prostate cancer are not well characterized, and the potential prognostic significance of serum half-lives and of serum doubling times is unclear. This study was designed to address those issues.
One hundred fifty-four patients with at least four serial PSA determinations who received external-beam radiation therapy alone were analyzed to determine PSA kinetics and to correlate kinetic parameters with outcome. Nonlinear regression techniques were used to estimate PSA half-lives and doubling times.
The PSA data fitted well to exponential models consistent with the hypothesis that PSA kinetics after radiation follow first-order (exponential) kinetics. The mean PSA half-life was 1.9 months (range, 0.5 to 9.2 months). No significant correlation existed between half-life and grade, stage, acid phosphatase level, serum testosterone level, or patient age. A weak correlation between half-life and pretreatment PSA level was observed: patients with low PSA levels tended to have longer half-lives. Half-life did not correlate with disease relapse or with the likelihood of developing a rising PSA profile. PSA doubling time in 37 patients with rising values ranged from 1.6 to 53 months (mean, 12.5 months). Doubling times were significantly longer than half-lives by an average factor of 6.5 and there was no correlation between half-life and subsequent doubling time. Doubling times were longer in low-grade tumors.
Serum kinetics of PSA in particular its rate of fall after radiation provide little, if any, useful clinical information. It is possible that serum kinetics of PSA are related to tumor cell kinetics but such relationships remain speculative. Correlative cell kinetic--PSA kinetic studies are needed to elucidate the mechanisms underlying the changes in PSA level after radiation therapy.
前列腺癌放射治疗后前列腺特异性抗原（PSA）的血清动力学特征尚不明确，血清半衰期和血清倍增时间的潜在预后意义也不清楚。本研究旨在解决这些问题。
对154例仅接受外照射放疗且至少有4次连续PSA测定的患者进行分析，以确定PSA动力学，并将动力学参数与预后相关联。采用非线性回归技术估计PSA半衰期和倍增时间。
PSA数据与指数模型拟合良好，这与放射治疗后PSA动力学遵循一级（指数）动力学的假设一致。PSA平均半衰期为1.9个月（范围为0.5至9.2个月）。半衰期与分级、分期、酸性磷酸酶水平、血清睾酮水平或患者年龄之间无显著相关性。观察到半衰期与治疗前PSA水平之间存在弱相关性：PSA水平低的患者半衰期往往较长。半衰期与疾病复发或PSA水平升高的可能性无关。37例PSA值升高患者的PSA倍增时间为1.6至53个月（平均12.5个月）。倍增时间明显长于半衰期，平均相差6.5倍，且半衰期与随后的倍增时间之间无相关性。低级别肿瘤的倍增时间较长。
PSA的血清动力学，尤其是放疗后其下降速率，几乎没有提供有用的临床信息。PSA的血清动力学可能与肿瘤细胞动力学有关，但这种关系仍属推测。需要进行相关的细胞动力学 - PSA动力学研究，以阐明放疗后PSA水平变化的潜在机制。
