In the largest prospective study of
cigarette smoking and colorectal cancer mortality, American Cancer Society
staff researchers report finding strong evidence for classifying cancers of
the colon and rectum as, in part, smoking-related.
An analysis of the Society's Cancer Prevention Study II, detailed in an
article in the December 6th edition of the Journal of the National Cancer
Institute, concludes that not only is long-term cigarette smoking associated
with an elevated risk for dying of this cancer, it estimates that about 12% of
the l997 deaths from colorectal cancer may be attributable to cigarette
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.
Male current smokers had a 32% higher death rate than non-smokers in the
study, and current female smokers had a higher death rate of 41%. The higher
death rates increased with duration of their habit and with the number of
cigarettes smoked daily.
The rates were higher for current smokers who began smoking cigarettes at
younger ages, than those who smoked longer and more cigarettes per day.
Cancer Prevention Study II began enrolling approximately one million
Americans in l982. Dr. Chao and her co-authors analyzed data on 312,332 men
and 469,019 women from CPS II, among which 4,432 died from either colon or
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 percent in l997, 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 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 '50s, '60s and '70s with
male rates being higher than female rates. As the smoking rates increased for
women, the colorectal rates became very similar for both genders," explained