Most significant effect was seen after 30 years of smoking, researchers say,,,,
TUESDAY, Dec. 16 (HealthDay News) -- Adding to the long list of cancers caused by smoking, Italian researchers report that the risk of getting colorectal cancer is higher in smokers, as is the risk of dying from that disease.
Smoking increases the risk of developing colorectal cancer by about 18 percent and the risk of dying from the malignancy by about 25 percent, according to the study, which was published in the Dec. 17 issue of the Journal of the American Medical Association.
"Smoking is significantly associated with colorectal cancer incidence and mortality," said the study's lead author, Edoardo Botteri, a biostatistician in the division of epidemiology and biostatistics at the European Institute of Oncology in Milan, Italy.
"People should be aware that smoking increases the risk of cancer not only in organs where there is direct contact with tobacco-related carcinogens, such as lung, oropharynx, larynx and upper digestive tract, but also in organs where exposure to tobacco degradation products is indirect, such as the pancreas, kidney, bladder, cervix, colon and rectum," explained Botteri.
Tobacco is responsible for about 100 million deaths during the past century and more than 5 million deaths a year, according to background information in the study. Yet, the study pointed out, there are still more than 1 billion smokers worldwide. Eighty percent of lung cancers are directly attributable to smoking, reports the study.
However, the connection to colorectal cancer isn't as conclusive.
To assess whether or not there is, in fact, a link, Botteri and his colleagues analyzed data from 106 observational studies that varied from small trials containing just several hundred participants to very large trials with more than 1 million participants.
When the researchers looked at the pooled risk, they found that smoking was associated with an 18 percent rise in the odds of getting colorectal cancer.
And, Botteri added, "There was an increase in risk with increasing number of cigarettes per day and pack-years -- the number of packs of cigarettes smoked per day multiplied by years of consumption."
The increased risk began after about 10 years of smoking and increased until it reached statistical significance after 30 years.
"That doesn't mean that there is no increased risk for people who smoked less than 30 years," noted Botteri, "It just means that there is strong evidence that exposure of 30 years or more increases the risk of colorectal cancer."
The researchers also found that smoking increased the risk of death from colorectal cancer by 25 percent.
Dr. Michael Thun, vice president emeritus of epidemiology and surveillance research at the American Cancer Society, said the study will be of most interest to researchers that study colon cancer, and he doesn't believe the findings will change screening recommendations.
Another message remains the same, he added: "With or without a relationship to colorectal cancer, the message is to avoid all forms of tobacco."
Botteri, however, believes that doctors should be "more vigilant" about making sure that smokers are compliant with current screening recommendations, and that perhaps, the initial screening age should be lowered for smokers.
Learn more about the risk factors for colorectal cancer from the American Cancer Society.
SOURCES: Edoardo Botteri, M.Sc., biostatistician, European Institute of Oncology, Milan, Italy; Michael Thun, M.D., vice president emeritus, epidemiology and surveillance research, American Cancer Society, Atlanta; Dec. 17, 2008, Journal of the American Medical Association
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