Most people understand the link between smoking and lung cancer, but researchers are learning even casual smokers are increasing their risk for other cancer types as well.
Case in point: Smoking increases the risk for developing colorectal cancer, and female smokers may have a greater risk than male smokers, according to data published in Cancer Epidemiology, Biomarkers & Prevention, a journal of the American Association for Cancer Research.
Dr. Inger Torhild Gram, professor in the Department of Community Medicine at the University of Tromsø in Norway, wanted to know why the number of new colon cancer cases per year has exploded during the last 50 years for men and women.
During her study she and her colleagues found startling new evidence to suggest women who smoke less than men still get more colon cancer.
“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 in a written statement.
Colorectal cancer is the third most commonly diagnosed cancer and the second leading cause of cancer death in men and women combined in the United States, according to the National Cancer Institute (NCI), part of the U.S. National Institutes of Health. About 72 percent of cases arise in the colon and about 28 percent in the rectum.
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“A causal relationship between smoking and colorectal cancer has recently been established by the International Agency for Research on Cancer of the World Health Organization, but unfortunately, this is not yet common knowledge, neither among health personnel nor the public,” she said.
The American Cancer Society estimates that 142,820 people will be diagnosed with colon cancer in 2013 and that 50,830 will die from colon cancer in the United States.
It’s important to note that while colorectal cancer can be extremely deadly, it’s also one of the most preventable cancer types.
If everyone who is 50 years old or older were regularly screened for colorectal cancer, as many as 60 percent of deaths from this cancer could be avoided, according to the NCI.
To examine the association between cigarette smoking and colon cancer, by tumor location, Gram and her colleagues looked at data for a large Norwegian study of more than 600,000 men and women.
The participants from four surveys initiated by the National Health Screening Service of the Norwegian Institute of Public Health had a short health exam and completed questionnaires about smoking habits, physical activity and other lifestyle factors.
The participants were followed by linkage to the Cancer Registry of Norway and the Central Population Register. During an average 14 years of follow-up, close to 4,000 new colon cancer cases were diagnosed.
Gram and her colleagues found, for the first time, that female smokers had a 19 percent increased risk compared with never-smokers, while male smokers had an 8 percent increased risk compared with never-smokers.
In addition, women who started smoking when they were 16 or younger and women who had smoked for 40 years or more had a substantially increased risk, by about 50 percent.
The study also show the number of cigarettes smoked per day, number of years smoked and number of pack-years smoked increased a woman’s colon cancer risk more than men.