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一项针对3,450件病例的检验发现，相较于从未吸烟者，目前正在吸烟的人被诊断罹患大肠癌的时间早了7年；这项研究也是第一个检验暴露在二手烟之下，特别是在年轻的时候，与较早发生大肠癌之间关系的研究。
这项研究线上发表于2月9日的癌症研究与临床肿瘤学期刊。
主要作者Luke J. Peppone博士，他是纽约罗彻斯特大学James P. Wilmot癌症中心的放射腺肿瘤学研究助理教授，他表示，这项研究结果所透露出来对医师与病患的讯息是很清楚的：当决定何时进行大肠癌筛检时，你应该将吸烟史、家族史与年龄列入考虑。
Peppone博士的团队检验来自1957年至1997年之间于纽约水牛城罗斯威尔公园癌症机构（RPCI）被诊断罹患大肠癌患者的资料（Peppone博士于2007年从RPCI加入罗彻斯特大学，其他共同作者皆来自RPCI）。
结果显示，在40年之间，吸烟习惯出现变化，目前或正在吸烟者的比例下降，而过去吸烟者的比例增加；目前正在吸烟者诊断出大肠癌的年龄比曾是吸烟者早了6.8年，且比戒烟不超过5年的人们早了4.3年；戒烟超过5年的人们风险增加并不显著。
然而，在青少年时期（17岁以下）时就开始吸烟或是烟吸得很多的（每天1包以上）人们，相较于从未吸烟者，被诊断罹患癌症的年龄显著较低；过去暴露在二手烟环境下是额外的危险因子。Peppone博士表示，事实上，当目前正在抽烟与吸二手烟的人合并分析，诊断罹患癌症的年龄早了将近10年。
虽然吸烟是许多癌症一个广为人知的危险因子，最近的研究指出，香烟可能造成大肠癌。
吸烟与大肠癌风险之间的关连性，其生物机转目前并不清楚；然而，研究者相信吸烟会降低人体对抗恶性肿瘤的能力，就像吸烟会降低整体免疫反应、使人们对抗感染与病毒的能力下降；吸烟所带来的致癌物质会透过血流、或是烟雾被吞下而到达肠胃道。
大肠直肠癌是男性与女性之间第三常见的癌症；研究显示，基因异常占了10%的新案例，然而，超过75%的案例是来自于散发突变以及／或是环境与生活型态因子，例如吸烟、饮食习惯不佳、喝酒、缺乏运动与肥胖。
国家癌症机构赞助这项研究。
Smokers Might Benefit from Earlier Colon Cancer Screening
By Roxanne Nelson
Medscape Medical News
An examination of 3450 cases has found that current smokers were diagnosed with colon cancer approximately 7 years earlier than people who never smoked. The study is also among the first to link exposure to second-hand smoke, especially early in life, with a younger age for colon cancer onset.
The article was published online February 9 in the Journal of Cancer Research and Clinical Oncology.
"The message for physicians and patients is clear: When making decisions about colon cancer screening, you should take into account smoking history as well as family history of disease and age," said lead author Luke J. Peppone, PhD, research assistant professor of radiation oncology at the James P. Wilmot Cancer Center at the University of Rochester, in New York.
Peppone's group examined data from patients diagnosed with colorectal cancer between 1957 and 1997 at Roswell Park Cancer Institute (RPCI) in Buffalo, New York. (Peppone joined the University of Rochester in 2007, coming from RPCI. His coauthors are from RPCI.)
During the 40-year period, smoking habits changed, with a decrease in the percentage of current or active smokers and an increase in the percentage of former smokers. Still, the age at colon cancer diagnosis was 6.8 years younger among current smokers and 4.3 years younger among former smokers who quit less than 5 years earlier, the results showed. People who quit more than 5 years earlier had no significant increased risk.
However, people who reported starting smoking in their early teens (before age 17) or who smoked heavily (1 pack a day or more) were the most likely to be diagnosed with cancer much younger than their never-smoking counterparts. Past exposure to second-hand smoke was an additional significant risk factor. In fact, when active smokers and passive smoking were combined into 1 subgroup, the age at cancer diagnosis was nearly 10 years earlier, Peppone said.
Although smoking is a well-known risk factor for many cancers, only recent studies have suggested that cigarettes might cause colon cancer.
The biologic reasons for the association between cigarette smoke and colon cancer risk are unclear. However, researchers believe that cigarette smoke reduces the body's resistance to malignancies, just as smoking can depress immune function in general, impairing the ability to fight off infections and viruses. Carcinogens from smoke reach the bowel through direct circulation or through the intestines after smoke is swallowed.
Colorectal cancer is the third most commonly diagnosed cancer among men and women. Genetics account for about 10% of new cases, the study said, whereas more than 75% of the cases arise from sporadic mutations and/or environmental and lifestyle factors, such as smoking, poor diet, alcohol use, lack of exercise, and obesity.
The National Cancer Institute funded the research.
J Cancer Res Clin Oncol. Published online February 9, 2008. Abstract