Bresalier Robert S
The University of Texas MD Anderson Cancer Center, Houston, Texas 77030, USA.
Curr Opin Gastroenterol. 2008 Jan;24(1):48-50. doi: 10.1097/MOG.0b013e3282f31d36.
Chemoprevention provides an opportunity to complement screening for the prevention of colorectal neoplasia. Findings from prospective randomized trials often conflict with those of observational studies. This review discusses some of the possible reasons based on recent clinical trials.
A recent prospective randomized trial demonstrates that folic acid supplementation in patients with a previous history of colorectal adenomas does not reduce future colorectal adenoma risk, and may possibly increase the risk of colorectal neoplasia.
The results of prospective randomized human trials of chemopreventive agents have in many cases been less impressive or have conflicted with the results of observational studies. Issues to be considered are the timing of the intervention during multistep carcinogenesis, baseline levels in a given individual or population, the complexity of dietary interactions, dose-response effects, and the duration of study.
化学预防为补充筛查以预防结直肠肿瘤提供了机会。前瞻性随机试验的结果常常与观察性研究的结果相冲突。本综述基于近期临床试验讨论了一些可能的原因。
一项近期的前瞻性随机试验表明，既往有结直肠腺瘤病史的患者补充叶酸并不能降低未来患结直肠腺瘤的风险，甚至可能增加患结直肠肿瘤的风险。
化学预防药物的前瞻性随机人体试验结果在很多情况下并不那么令人印象深刻，或者与观察性研究的结果相冲突。需要考虑的问题包括多步骤致癌过程中干预的时机、特定个体或人群的基线水平、饮食相互作用的复杂性、剂量反应效应以及研究持续时间。
