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.
SOURCES: Michael J. Thun, M.D., vice president emeritus, epidemiology and surveillance research, American Cancer Society; Michael John Hall, M.D., director, gastrointestinal risk assessment program, Fox Chase Cancer Center, Philadelphia; Peter S
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