Smoking has been consistently associated with an increased risk of colorectal adenomas and hyperplastic polyps as well as colorectal cancer.
Conversely, nonsteroidal anti-inflammatory drugs (NSAID) have been associated with reduced colorectal cancer risk.
Dr Polly Newcomb and colleagues from Seattle evaluated the joint association between smoking and regular NSAID use with colorectal cancer risk.
The team examined these associations stratified by tumor microsatellite instability.
The research team conducted a population-based case-control study.
The team analyzed 1792 incident colorectal cancer cases and 1501 population controls in the Seattle area from 1998 to 2002.
Microsatellite instability, defined as microsatellite instability high or low/microsatellite stable, was assessed in tumors of 1202 cases.
Compared with nonsmokers, colorectal cancer risk was modestly increased among individuals who had ever smoked.
|Smokers of long duration were at elevated risk even with NSAID use|
The researchers found that current NSAID use was associated with a 30% lower risk compared with nonusers.
There was a statistically significant interaction between smoking duration and use of NSAIDs.
Relative to current NSAID users who never smoked, those who both smoked for 40 years or more and had never used NSAIDs were at the highest risk.
There was a stronger association within microsatellite high instability tumors with current smoking than there was within microsatellite low stability/stable tumors.
The researchers observed that smokers of long duration were at elevated risk of microsatellite high instability tumors even with NSAID use.
The risk of microsatellite low instability/stable tumors was not elevated among long-duration smokers with long exposure to NSAIDs.
However, the researchers noted that it was elevated among long-duration smokers who had never used NSAIDs.
Dr Newcomb's team concludes, “There seems to be a synergistic inverse association, implying protection, against colorectal cancer overall as a result of NSAID use and non-smoking.”
“However, risk of microsatellite high instability colorectal cancer remains elevated among smokers even when they have a history of NSAID use.”