Smoking & colon polyp

It is known that smoking causes lung cancer and heart disease. Does smoking play a role in causing colorectal cancer (CRC)? While there are well known genetic causes for CRC, most CRCs in the general population are not genetically linked. Colonic adenomatous polyps are precursors to CRC; the larger the polyp, the higher the chance that it will have malignant potential. Colorectal polyps can be pedunculated or flat. Pedunculated polyps are easier to visualise and flat polyps can be missed easily during colonoscopy, especially when they are small. If adenomatous polyps are left untreated, they will turn into colon cancer with time. Recently, the American College of Gastroenterology published guidelines suggesting that smokers with a history of > 20 pack years may need screening for CRC earlier than their non-smoking counterparts. Are smokers at higher risk of developing colon polyps?

Researchers from Seoul National University Hospital studied 5254 asymptomatic subjects undergoing screening colonoscopy (J Gastroenterol Hepatol 2010; 25: 519 – 525). They were split into 3 groups aged 30 – 39 years, 40 – 49 years and 50 – 59 years. The prevalence of overall adenomas was 10.4% in the 30- 39 years age group, 22.2% in the 40 – 49 years age group and 32.8% in the 50 – 59 years age group. The prevalence of advanced adenoma was 0.7%, 2.7% and 4.1%, respectively. Male sex, current smoker and family history of CRC were independent predictors of advanced adenoma in the 40 - 49 years group. The risk of developing advanced adenoma in smokers is increased by 58%.

In another study from the University of Connecticut, 600 asymptomatic patients presenting for CRC screening were studied with high-definition colonoscope to detect flat adenomas (Gastrointest Endosc 2010; 71: 1234 – 1240). Of these 600 patients, 313 were non-smokers, 115 were heavy smokers (10 or more pack years and still smoking or had quit within 10 years) and 172 were low-exposure smokers (< 10 pack years or had quit more than 10 years ago). Heavy smoking increased the risk for flat adenomas of any size by 153%. The risk for flat adenomas of 6 mm or more was increased 284% in heavy smokers. Heavy smoking increased the risk of advanced flat adenomas by 181%. How heavy you smoke also increased the risk of developing flat adenomas. The risk was increased 128 % in those with > 30 pack years of smoking compared to those with < 30 pack years.

Smoking is known to cause many health problems. It is also considered to be an anti-social behaviour by many. Yet the number of smokers worldwide is increasing, especially in developing and under-developed countries. The mind boggles!