In the largest prospective study of cigarette smoking and colorectal cancer mortality, researchers from the American Cancer Society report finding strong evidence that cancers of the colon and rectum are, in part, smoking related.
An analysis of the American Cancer Society’s Cancer Prevention Study II appeared in a recent issue of the Journal of the National Cancer Institute (92:1888-1896, 2000). It concluded that not only is long-term cigarette smoking associated with an elevated risk of dying of colorectal cancer, but that about 12% of 1997 deaths from this cancer may be attributable to cigarette smoking.
Lowest Rates Among Nonsmokers
Ann Chao, PhD, Michael J. Thun, MD, and colleagues at the American Cancer Society report that colorectal death rates were highest among current smokers and lowest among those who never smoked. "Clear benefits were also observed among those people who had quit smoking; the longer ago, the higher the benefit," said Dr. Chao.
In the study, current male smokers had a 32% higher death rate than nonsmokers, and current female smokers had a death rate of 41%. The higher death rates increased with duration of the habit and with the number of cigarettes smoked daily.
The rates were higher for current smokers who began smoking cigarettes at younger ages, than among those who smoked longer and more cigarettes per day.
The Cancer Prevention Study II began enrolling approximately 1 million Americans in 1982. Dr. Chao and her coauthors analyzed data on 312,332 men and 469,019 women, among whom 4,432 died from either colon or rectal cancer. Data from these participants were controlled for a number of potentially confounding variables including alcohol(Drug information on alcohol) use, physical activity, family history of colorectal cancer, vitamin use, and dietary factors.
"The size of the study allowed us to examine, in detail, gradients in smoking behavior separately in former and current smokers," said Dr. Chao. "It also permitted us to estimate the percentage of smoking-related colorectal cancer deaths in the general population, which would have been about 12% in 1997, or more than 6,800 people for that year," she said.
"The smoking epidemic in women began decades later than in men," said Michael J. Thun, MD, vice president of epidemiology and surveillance research for the American Cancer Society. "This may explain, in part, why the trends in colorectal cancer incidence and death rates differed between genders during the 1950s, 1960s, and 1970s, with male rates being higher than female rates. As the smoking rates increased for women, the colorectal rates became very similar for both genders," said Dr. Thun.