Miller A B
J Cancer Res Clin Oncol. 1991;117(3):177-85. doi: 10.1007/BF01625422.
Primary prevention of cancer requires control of both involuntary and voluntary exposures. Involuntary exposures include carcinogens in air and water, and various forms of radiation. Often these exposures are difficult to characterise individually and difficult to study epidemiologically. Although it is unlikely that they account for more than a small proportion of cancers, it is important that we refine our techniques of study to facilitate their control. Voluntary (lifestyle) exposures are responsible for the majority of cancers. In many developed countries, tobacco accounts for approximately 30% of cancer deaths, and major public health endeavours are justified to reduce this toll. Dietary factors may be as important, with dietary fat the most important risk factor, vegetables and fruits being protective. In several studies, including a cohort study in Canada, dietary fat increases breast cancer risk, though other studies have been negative. The evidence for fat increasing the risk of colorectal is more consistent. Epidemiology has shown that secondary prevention of cancer is applicable by screening for breast cancer with mammography with or without physical examination in women age 50-69, and screening for cervix cancer in women age 25-60 with cervical cytology. Organised screening programmes are essential to ensure that a high proportion of women are screened, and that the tests are high quality with adequate quality control. Under these circumstances screening every 2 years for breast cancer and every 3 years for cervix cancer is cost-effective. Screening for other cancers cannot be recommended currently. There is a time to effect that must be recognised in planning primary or secondary prevention. Full effect of most primary activities will not be achieved for decades, screening may require a decade. Available knowledge must be applied now, however, to ensure the effect will eventually be seen, as is now occurring in some countries with the downturn in lung cancer mortality following smoking reduction in men.
癌症的一级预防需要控制非自愿和自愿接触。非自愿接触包括空气和水中的致癌物以及各种形式的辐射。通常，这些接触难以单独描述，也难以进行流行病学研究。尽管它们导致的癌症不太可能超过一小部分，但我们改进研究技术以促进对其控制非常重要。自愿（生活方式）接触是大多数癌症的原因。在许多发达国家，烟草导致约30%的癌症死亡，因此开展重大公共卫生行动以降低这一死亡人数是合理的。饮食因素可能同样重要，饮食脂肪是最重要的风险因素，蔬菜和水果则具有保护作用。在包括加拿大一项队列研究在内的多项研究中，饮食脂肪会增加患乳腺癌的风险，不过其他研究结果为阴性。脂肪增加结直肠癌风险的证据更为一致。流行病学表明，癌症的二级预防适用于对50至69岁女性进行乳房X线摄影筛查乳腺癌，无论是否进行体格检查，以及对25至60岁女性进行宫颈细胞学检查筛查宫颈癌。有组织的筛查计划对于确保高比例的女性接受筛查以及确保检测质量高且有足够的质量控制至关重要。在这种情况下，每2年筛查一次乳腺癌，每3年筛查一次宫颈癌具有成本效益。目前不建议对其他癌症进行筛查。在规划一级或二级预防时，必须认识到存在一个生效时间。大多数一级预防活动的全面效果在几十年内都无法实现，筛查可能需要十年时间。然而，现在必须应用现有知识，以确保最终能看到效果，就像现在一些国家因男性吸烟减少导致肺癌死亡率下降那样。
