Moyad M A
Department of Surgery, University of Michigan Medical Center, Ann Arbor 48109-0330, USA.
Semin Urol Oncol. 2001 Nov;19(4):232-46.
Randomized controlled trials are generally regarded as the standard of study designs to determine potential causality. The inclusion of a placebo group in these trials, when appropriate, is generally needed to access the efficacy of a drug or dietary supplement. The recent increasing use of dietary supplements and herbal medications by patients makes it imperative to reevaluate the past findings of clinical studies. Several large-scale trials of dietary supplements have been tested in various populations to determine their effect on cancer prevention. Other trials have focused on patients already diagnosed with cancer. In the latter case, it is difficult to involve a placebo because of the serious nature of the disease. Nevertheless, much has been gleaned from these trials directly and indirectly. Overall, when analyzing primary endpoints in these trials, the results have been discouraging and even support the nonuse of certain supplements because of potential adverse effects. Other secondary endpoints in these same trials have revealed some potential encouraging and discouraging data. Individuals who currently qualify for the potential use of dietary supplements for cancer may be restricted to those who have a deficiency in a certain compound despite adequate dietary sources or lifestyle changes. Those individuals with a smoking history or other unhealthy lifestyle seem to have the most to gain or lose from taking certain dietary supplements for cancer. The time seems more than ripe to evaluate past adequate trials with supplements, such as beta-carotene, N-acetyl-cysteine, selenium, shark cartilage, vitamin C, vitamin E, and others. Again, these studies have been disappointing, but they provide insight for the clinician and patient of what to potentially expect when using these supplements for cancer. In addition, indirect trials for other conditions (cardiovascular) may provide future insight into possible results for future cancer prevention trials.
随机对照试验通常被视为确定潜在因果关系的研究设计标准。在这些试验中，适当时通常需要纳入安慰剂组来评估药物或膳食补充剂的疗效。患者对膳食补充剂和草药药物的使用近来日益增加，因此必须重新评估临床研究过去的结果。已经在不同人群中对几种膳食补充剂进行了多项大规模试验，以确定它们对癌症预防的作用。其他试验则聚焦于已被诊断患有癌症的患者。在后一种情况下，由于疾病的严重性，很难纳入安慰剂组。然而，从这些试验中已经直接或间接地获得了很多信息。总体而言，在分析这些试验的主要终点时，结果令人沮丧，甚至支持不使用某些补充剂，因为可能存在不良反应。这些相同试验中的其他次要终点也揭示了一些可能令人鼓舞和令人沮丧的数据。目前有资格潜在使用膳食补充剂预防癌症的个体可能仅限于那些尽管有充足的饮食来源或生活方式改变但仍缺乏某种化合物的人。那些有吸烟史或其他不健康生活方式的人似乎从服用某些预防癌症的膳食补充剂中获益或损失最大。现在似乎是时候评估过去关于补充剂的充分试验了，比如β-胡萝卜素、N-乙酰半胱氨酸、硒、鲨鱼软骨、维生素C、维生素E等等。同样，这些研究令人失望，但它们为临床医生和患者提供了在使用这些补充剂预防癌症时可能预期的情况的见解。此外，针对其他病症（心血管疾病）的间接试验可能会为未来癌症预防试验的可能结果提供未来的见解。
