THURSDAY, Dec. 3, 2009 (HealthDay News) -- Add colorectal cancer to the list of malignancies caused by smoking, with a new study strengthening the link between the two.
And other studies are providing more bad news for people who haven't managed to quit: Two papers published in the December issue of Epidemiology, Biomarkers & Prevention, a themed issue on tobacco, strengthen the case for the dangers of secondhand smoke for people exposed to fumes as children and as adults.
Inhaling those secondhand fumes may raise a woman's odds for breast cancer or a child's lifetime risk for lung malignancies, the studies found.
All of the findings, while grim, could be useful in the war against smoking, experts say.
"With the FDA [U.S. Food and Drug Administration], we're hoping this will be a significant tool to controlling tobacco, although it could get bogged down in so many different ways," said Dr. Peter Shields, deputy director of the Georgetown University Lombardi Comprehensive Cancer Center and senior editor of the journal in which these papers appeared. "The FDA is going to have to make a lot of tough decisions about how to regulate tobacco, and the more science they have will help them."
Is this latest round of revelations going to change current screening recommendations? Probably not, at least not yet, Shields added.
One study found that long-term smokers have a higher risk of developing colorectal cancer, a finding that factored into the recent decision by the International Agency for Research on Cancer (IARC) to assert that there is "sufficient" evidence to link the two, up from its previous "limited" evidence.
"It took a long time to figure this out because the relationship [between smoking and colorectal cancer] is not as strong [as for some other cancers]," said Dr. Michael Thun, senior author of the study and vice president emeritus of epidemiology and surveillance research at the American Cancer Society. "The question was, is the association we're seeing really caused by smoking?"
The researchers managed to adjust for other colorectal cancer risk factors, such as not getting screened, obesity, physical activity and eating a lot of red or processed meats. The issue is tricky because people who smoke are already more likely to engage in these types of behavior.
"When they took all of those other things out, smoking was still a small, elevated risk," said Dr. Michael John Hall, director of the gastrointestinal risk assessment program at Fox Chase Cancer Center in Philadelphia.
"We already know that smoking is bad. That doesn't change. A positive thing that comes out of this is that if you can stop smoking earlier, you eliminate your risk later on, but the more you smoke, the risk is higher."
This large prospective study, which followed almost 200,000 people over 13 years, found that current smokers had a 27 percent increased risk of colorectal cancer and former smokers a 23 percent increased risk compared with people who had never smoked.
People who had smoked for at least half a century had the highest risk -- 38 percent higher than never smokers -- of developing colorectal cancer
The good news is that people who tossed their cigarettes before the age of 40 or who had not smoked for 31 or more years had no increased risk.
Two other studies focused on the risk of secondhand smoke, or passive smoking. In one, children exposed to secondhand smoke had a higher risk of developing lung cancer as adults, researchers from institutions including the U.S. National Cancer Institute found. In another, California researchers found that adult non-smoking women who had spent long periods of time in smoking environments upped their odds of developing postmenopausal breast cancer.
The breast cancer findings were seen mostly in postmenopausal women, with a 17 percent higher risk for those who had had low exposure, a 19 percent increased risk for those with medium exposure and a 26 percent increased risk for those who had high long-term exposure over their lifetime.
Adult exposure, such as spending time in smoking lounges where others were smoking, carried the most risk, with childhood exposure appearing negligible.
For children exposed to smokers, the odds of developing lung cancer was notably higher among individuals with a specific mutation on the MBL2 gene, the other study found.
Passive smoking during early life more than doubled the risk of lung cancer among people who had never smoked, the researchers found. They noted that the risk from secondhand smoke was even higher than that noted in the U.S. Surgeon General's report. The risk was 2.5 times higher among those with this genetic signature.
In another study, people who smoked cigarettes and drank alcohol after a diagnosis of head and neck cancer had a worse prognosis than those who abstained from these habits, according to researchers at Yale University School of Medicine and Yale's School of Public Health, among others.
Previous research had shown that smoking and drinking alcohol before a diagnosis meant the patient was more likely to die from the cancer.
With the new classification on smoking causing colorectal cancer, 17 cancers are now attributed to smoking.
The American Cancer Society has more on tobacco and cancer.