Colorectal cancer survivors who smoke cigarettes were at more than twice the risk of death than non-smoking survivors, adding to existing evidence that cigarette smoking is associated with higher all-cause and colorectal cancer-specific mortality. The findings come from a new study by American Cancer Society researchers, one of the largest studies of smoking and colorectal cancer survival and the first study to prospectively collect both pre- and post-diagnosis smoking information. It is published early online in the Journal of Clinical Oncology.
Existing evidence links smoking with higher chances of being diagnosed with colorectal cancer, but its association with survival after colorectal cancer diagnosis is unclear.
To investigate the association of smoking, before and after diagnosis, with all-cause and colorectal cancer-specific mortality among colorectal cancer survivors, researchers led by Dr. Peter Campbell identified 2,548 people newly diagnosed with invasive, non-metastatic colorectal cancer from among 184,000 adults in the American Cancer Society’s Cancer Prevention Study II. Among the 2,548 colorectal cancer survivors, 1,074 died during an average of 7.5 years of follow-up time, including 453 as a result of colorectal cancer.
The researchers found those who were smokers before diagnosis had more than twice the risk of death from all causes (relative risk [RR] = 2.12) as well as from risk of dying of colorectal cancer (RR, 2.14).
Former smoking before diagnosis was associated with higher all-cause mortality (RR, 1.18) but not with colorectal cancer-specific mortality. Smoking after diagnosis was also associated with more than double the risk of overall mortality (RR, 2.22) over the course of the study, and was associated with nearly twice the risk of colorectal cancer-specific mortality (RR, 1.92).
There is a long established link between cigarette smoking and lung cancer, but new research shows there is also a link between smoking and colon cancer, especially for women.
In an article published this month in Cancer Epidemiology Biomarkers and Prevention, researchers in Norway followed more than 600,000 men and women and found that female smokers had a 19 percent increased chance of developing colon cancer over non-smokers. Male smokers had an 8 percent increased chance of developing colon cancer over non-smokers.
“Globally, during the last 50 years, the number of new colon cancer cases per year has exploded for both men and women,” said Inger Torhild Gram, M.D., Ph.D., professor in the Department of Community Medicine at the University of Tromsø in Norway and one of the study’s authors. “Our study is the first that shows women who smoke less than men still get more colon cancer.”
The study concluded that female smokers might be more susceptible especially to proximal or left sided colon cancers than male smokers. “The finding that women who smoke even a moderate number of cigarettes daily have an increased risk for colon cancer will account for a substantial number of new cases because colon cancer is such a common disease,” said Gram.
Women smokers who are inspired by this latest research to quit may actually have a tougher time kicking the habit than men.
The authors say it is plausible that smokers have pathologically more-aggressive tumors, or that smoking may decrease the efficacy of colorectal cancer treatment. “Further research is needed to understand mechanisms whereby smoking may increase colorectal cancer-specific mortality and determine if quitting smoking after diagnosis lowers the risk of colorectal cancer-specific mortality,” the authors conclude.
Citation: Active Smoking and Mortality Among Colorectal Cancer Survivors: The Cancer Prevention Study II Nutrition Cohort. Baiyu Yang, Eric J. Jacobs, Susan M. Gapstur, Victoria Stevens, and Peter T. Campbell. JCO published online on February 2, 2015; DOI:10.1200/JCO.2014.58.3831
Colorectal cancer is not strictly considered a tobacco-related malignancy, but modest associations have emerged from large meta-analyses. Most studies, however, use self-reported data, which are subject to misclassification. Biomarkers of tobacco exposure may reduce misclassification and provide insight into metabolic variability that potentially influences carcinogenesis. Our aim was to identify metabolites that represent smoking habits and individual variation in tobacco metabolism, and investigate their association with colorectal cancer. In a nested case-control study of 255 colorectal cancers and 254 matched controls identified in the Prostate, Lung, Colorectal and Ovarian cancer screening trial, baseline serum was used to identify metabolites by ultra-high-performance liquid-phase chromatography and mass spectrometry, as well as gas chromatography with tandem mass spectrometry. Odds ratios (OR) and 95% confidence intervals (CI) were estimated by logistic regression. Self-reported current smoking was associated with serum cotinine, O-cresol sulfate and hydroxycotinine. Self-reported current smoking of any tobacco (OR = 1.90, 95% CI: 1.02-3.54) and current cigarette smoking (OR = 1.51, 95% CI: 0.75-3.04) were associated with elevated colorectal cancer risks, although the latter was not statistically significant. Individuals with detectable levels of hydroxycotinine had an increased colorectal cancer risk compared with those with undetectable levels (OR = 2.68, 95% CI: 1.33-5.40). Although those with detectable levels of cotinine had a suggestive elevated risk of this malignancy (OR = 1.81, 95% CI: 0.98-3.33), those with detectable levels of O-cresol sulfate did not (OR = 1.16, 95% CI: 0.57-2.37). Biomarkers capturing smoking behavior and metabolic variation exhibit stronger associations with colorectal cancer than self-report, providing additional evidence for a role for tobacco in this malignancy.
Published by Oxford University Press 2014.
American Cancer Society
Journal - Journal of Clinical Oncology
Funder - American Cancer Society