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Smoking increases mortality risk in patients with colorectal cancer
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Cigarette smoking is associated with a higher mortality rate among patients with invasive, nonmetastatic colorectal cancer, according to results of a study led by investigators from the American Cancer Society.
The International Association for Research on Cancer added colorectal cancer to the list of smoking-attributable cancers in 2009. Five years later, the U.S. Surgeon General followed suit.
Although many studies have identified a relationship between smoking and the incidence of colorectal cancer — specifically with certain phenotypes of the disease, such as BRAF mutation-positive, microsatellite instability and CpG island methylator phenotype — information about the effects of active smoking on survival rates after diagnosis was limited.
Peter T. Campbell, PhD, director of the tumor repository in the epidemiology research program at the ACS, and colleagues used the Cancer Prevention Study II cohort to investigate the association of active smoking before and after diagnosis of invasive, nonmetastatic colorectal cancer, as well as its effect on mortality.
All 2,548 adults were free of colorectal cancer at the time of study entry. They were diagnosed with invasive, nonmetastatic colorectal cancer between baseline (1992 or 1993) and 2009.
The mean age of participants was 65 years at baseline and 73 years at diagnosis.
Participants self-reported smoking habits on a baseline questionnaire, which was updated in 1997 and then every other year through the endpoint. Information about post-diagnosis smoking habits was available for 88.5% of the cohort.
Mean follow-up was 7.5 years (standard deviation, 4.6 years; range, 2 days to 18.1 years).
Researchers determined 1,074 participants (42.1%) died during follow-up, including 453 as a result of colorectal cancer. The other most frequent causes were cardiovascular disease (n = 201), respiratory system disease (n = 66) and lung cancer (n = 55).
Using multivariable adjusted Cox proportional hazards regression models, the investigators determined current smoking at the time of colorectal cancer diagnosis was associated with a higher rate of all-cause mortality (RR = 2.12; 95% CI, 1.65-2.74), as well as a higher rate of colon cancer-specific mortality (RR = 2.14; 95% CI, 1.5-3.07).
Patients classified as former smokers at the time of diagnosis demonstrated a higher all-cause mortality rate (RR = 1.18; 95% CI, 1.02-1.36), but they did not demonstrate a higher rate of colon cancer-specific mortality (RR = 0.89; 95% CI, 0.72-1.1).
Patients who continued to smoke after diagnosis demonstrated higher rates of all-cause mortality (RR = 2.22; 95% CI, 1.58-3.13) and colon cancer-specific mortality (RR = 1.92; 95% CI, 1.15-3.21).
“Smoking is associated with a nearly twofold higher risk of death compared with never smoking,” Campbell and colleagues wrote. “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.” – by Anthony SanFilippo
Disclosure: The researchers report no relevant financial disclosures.
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