NSAIDs may not reduce colorectal cancer risk in smokers

In a large, population-based study comparing risk factors in people with and without colorectal cancer, the researchers found the highest risk of colon cancer to be among long-term smokers aged 20 or older who had never used NSAIDs. The researchers also found that smokers who used NSAIDs were still at an approximate 30% higher risk of colon cancer than non-smokers.

The findings, which appear in Cancer Research, arise from the first study of its kind to examine the effects of NSAID use on colorectal-cancer risk among smokers.

In particular, the researchers were interested in examining the impact of NSAIDs on a certain type of colorectal tumor that may be associated with smoking. Such tumors display microsatellite instability, an acquired genetic characteristic that indicates defects in DNA-repair machinery. Microsatellite instability, or MSI, occurs in approximately 15% to 20% of colon cancers.

The researchers found a two-fold increased risk of microsatellite-unstable colorectal tumors among long-term smokers who took NSAIDs – about the same risk as smokers who had not used NSAIDs.

“Given the damage that smokers receive over their lifetime, even strong anti-progression agents, like NSAIDs, may be ineffective,” the authors wrote. “NSAIDs may not be able to counteract the long-term effects of smoking, as evidenced by our observation that long-term smokers are at increased risk of colorectal cancer, despite current NSAID use.”