Study links smoking, colorectal cancer

Newfoundland and Labrador has the highest incidence of colorectal cancer in Canada and the world, and now, a new study has linked this distinction to a historically high prevalence of tobacco use.

The study, conducted by a team of Memorial University faculty of medicine researchers, is the first large population-based study in Canada that shows a clear relationship between colorectal cancer and smoking. It was recently published in the Canadian Journal of Public Health.

Dr. Peter Wang, the study’s senior author, said the team’s research found cigarette smoking increased the risk of colorectal cancer among men and women, but it demonstrated a stronger effect for males than females.

Globally, colorectal cancer is the third leading cause of death from cancer in males and the fourth leading cause of death from cancer in females.

Wang said the incidence of colorectal cancer in Canada is around 60 cases per 100,000 population a year.

In Newfoundland and Labrador, it’s about 86 per 100,000, which he calls “very high.”

The study points out that Newfoundland and Labrador has had a high prevalence of tobacco use, with an average rate of 34 per cent during the period 1985 to 2003.

Wang said current tobacco use in the province is about 25 per cent of the population.

“But, fortunately,” he said, “we are seeing a declining trend.”

The study involved an investigation of 702 colorectal cancer cases, with participants recruited using the Newfoundland and Labrador Colorectal Cancer Registry.

The results from this group were compared to a control group of 717 people, ages 20 to 74, who were randomly selected.

It was noted in the research document that 258 of the 702 colorectal cancer patients are now deceased, including 143 who died before the actual survey was conducted, requiring responses from proxies.

“But, fortunately,” we are seeing a declining trend.” - Dr. Peter Wang

Wang said the living participants were all asked a series of questions about tobacco use.

He said the study found a significant association between smoking cigarettes and colorectal cancer. The findings showed a 49 per cent increased risk among all smokers, 36 per cent increased risk among former smokers, and 96 per cent higher risk among current smokers, compared to non-smokers.

Wang said the study also found a higher risk of colorectal cancer among people who consumed alcohol and who were former or current smokers, compared to non-smokers.

Overall, he said, the study indicated that the effects of smoking on colorectal cancer seemed to be stronger in males and alcohol drinkers and also demonstrated a slightly stronger effect on rectum rather than colon cancer. 

The role of alcohol in increased colorectal cancer incidence isn’t certain, Wang said, but it seems to be a co-factor with tobacco use.

The study points out that tobacco smoke contains at least 50 carcinogenic components, “the most genotoxic of which are thought to be polycyclic aromatic hydrocarbons, heterocyclic aromatic amines and N-nitroso compounds.”

Wang said the MUN researchers are planning to do more work in this area, looking at possible relationships between cancer and obesity, alcohol use and calcium and Vitamin B intake.

The latest study was supported by the Canadian Institutes of Health Research through an interdisciplinary team research grant on colorectal cancer.

dss@thetelegram.com