Washington, Feb 14 : A study at University of Rochester Medical Center, has suggested that screening for colorectal cancer, currently recommended to start at age 50 for most people, should start 5 to 10 years earlier for people with a significant lifetime exposure to tobacco smoke.
The study, led by Luke J. Peppone, Ph.D., research assistant professor of Radiation Oncology at the James P. Wilmot Cancer Center at the University of Rochester, examined 3,450 cases and found that current smokers were diagnosed with colon cancer approximately seven years earlier than the ones who never smoked.
This study is also one of the first to associate exposure to second-hand smoke, especially early in life, with a younger age for colon cancer onset.
"The message for physicians and patients is clear: When making decisions about colon cancer screening you should take into account smoking history as well as family history of disease and age," said Peppone.
The researchers also assessed data from patients having colorectal cancer between 1957 and 1997 at Roswell Park Cancer Institute in Buffalo. During this 40 years period, smoking habits changed, with a decrease in the pctage of current or active smokers and an increase in the pctage of previous smokers.
However, the age at colon cancer diagnosis was 6.8 years younger among current smokers and 4.3 years younger for former smokers who quit less than five years ago, the results showed. Also, those who quit more than five years ago had no significant increased risk.
However, people who reported they began smoking as young teens (before age 17) or who smoked heavily (1 pack a day or more) were the most likely to be diagnosed with cancer much younger than their never-smoking counterparts.
Peppone said that past exposure to second-hand-smoke was an additional, significant risk factor, as compared to never smoking. In reality, after combining active smokers and passive smoking into one subgroup, the age at cancer diagnosis was nearly 10 years earlier.
Though, smoking is a well-known risk factor for many cancers, it is only recently that studies have suggested that cigarettes may cause colon cancer. Also, the biological reasons behind the cigarette smoke-colon cancer risk are unclear.
However, it is thought that cigarette smoke reduces the body's resistance to malignancies, just like smoking can depress immune function in general, impairing the ability to fight off infections and viruses.
Carcinogens from smoke reach the bowel through direct circulation or by swallowing smoke and passing it through the intestines.Colorectal cancer is the third most commonly diagnosed cancer among men and women.
The study said that genetics account for about 10 pct of new cases, while more than 75 pct of the cases crop up from sporadic mutations and/or environmental and lifestyle factors such as smoking, a poor diet, alcohol use, lack of exercise and obesity.
The article appears online in the Journal of Cancer Research and Clinical Oncology.