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 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
"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.