The media has been buzzing about newly published data on the use of aspirin in patients with colon and rectal cancer. Since the 1980s, the genetic mechanism of colorectal cancer development has been known. Colon cells, called colonocytes, take a "hit" to one of their genes. The cells begin to grow abnormally, and they form disorganized tissue which can become a polyp. A second "hit" makes the cells even more irregular, and the polyp turns into a cancer. Although admittedly, this is a simplified version of the genetic mechanism, these are the genetic steps required for the development of cancer. Why does it happen to some people and not others?
The human body is complex. There is an interaction between a person’s immune system, the environment and genetics. These complex interactions are what determines who will develop cancer and who will not. We have known for some time about something called the inflammatory response. Basically, an increased inflammatory response may actually worsen injury – think keloid formation – the body tries so hard to heal it forms bigger scars as the cells grow more.
This response is mediated by a protein called Cox-2. This protein is stimulated during an inflammatory response, and Cox-2 also stimulates cellular growth. That is why the inflammatory response also promotes colon polyp and colon cancer growth – Cox-2 causes these cells to multiply at a faster rate.
This pathway has been extensively studied in patients with abdominal obesity (the metabolic syndrome), and the increased risk of colon cancer and polyps may be due in part to the increased production of Cox-2. Inhibiting Cox-2 has been studied for many years as a way to decrease cellular growth and reduce cancer risk.
Aspirin and NSAIDs (nonsteroidal anti-inflammatory drugs) decrease the inflammatory response and they inhibit Cox-II. That is why they are effective as pain relievers. The pain from an injury is due to the inflammatory response. This is also why aspirin benefits patients with coronary artery disease and heart attacks, as it decreases the injury to the blood vessels that supply the heart.
There have been prior studies in the New England Journal of Medicine and other journals showing aspirin use decreases polyp formation and may also reduce the risk of colon cancer. The study in this week’s JAMA showed that even after a diagnosis of colon cancer, aspirin use reduces the risk of dying from non-metastatic colon cancer by almost one third.
There are some caveats. Firstly, the aspirin used was full strength and not a baby aspirin, so there is the risk of side effects such as bleeding and GI problems. Second, not every colon cancer is caused by Cox-2, so the benefit is limited to those cancers that express the Cox-2 protein. That being said, I routinely recommend a daily aspirin to all of my patients that have had polyps or colorectal cancer. This study at least re-enforces this aspect of my practice, and tells us that an aspirin a day can keep some colorectal problems away.