A researcher from Boston, Massachusetts, USA, reviewed the epidemiological evidence on cigarette smoking and risk of colorectal cancer.
Edward Giovannucci, of the Brigham and Women's Hospital, and Harvard Medical School, assessed a number of studies.
21 out of 22 studies found that long-term heavy cigarette smokers have a 2- to 3-fold elevated risk of colorectal adenoma.
Risk of large adenomas, immediate cancer precursors, was elevated in smokers in 12 of 12 studies.
The studies of smoking and colorectal cancer risk conducted earlier in the twentieth century consistently did not show any association.
However, 27 studies in various countries, including the vast majority of those that have been analyzed in the past several years, showed an association between tobacco use and colorectal cancer.
|20% of colorectal cancers, in US, attributable to smoking.|
|Cancer Epidemiology Biomarkers and Prevention|
In the United States, 15 of 16 studies were found to demonstrate an association. These were conducted after 1970 in middle-aged men and elderly men, and, in the 1990s, in women.
Giovannucci notes that this temporal pattern is consistent with an induction period of 3 to 4 decades, between genotoxic exposure and the diagnosis of colorectal cancer. In addition, it is consistent with men having begun smoking several decades earlier than women.
"Overall, accumulating evidence, much within the past decade, strongly supports the addition of colorectal cancer to the list of tobacco-associated malignancies.
"It also endorses the possibility that up to one in five colorectal cancers in the United States may be potentially attributable to tobacco use," he concludes.