Aspirin, colon cancer, and genetics

I don’t usually blog about cancer risks, mainly because I don’t want to alarm anyone unnecessarily. There are lots of very common genetic variants that add just a little bit to your risk for cancer, but the bigger picture for most cancers seems to be environmental factors.

But I’m breaking my “no cancer” blogging rule today to talk about a cancer prevention option may be worthwhile for you, depending on your genetic variants. As always, I encourage you to do your own research on this topic before taking action.

Colon Cancer
Colon cancer is one of the most common forms of cancer, with a lifetime risk of about 5%.  Survival rates are high for those who detect it early, while late stage, metastasized colon cancer is often deadly. [ref]

Aspirin, a drug that is cheap and in use for a hundred+ years, has been in the news lately as possibly preventing several types of cancer, including colon cancer.  But the jury is still out on whether or not to recommend aspirin to everyone as a way to prevent cancer.  The American Cancer Society is currently still reviewing the issue, although it does note that a 2011 meta-analysis showed that daily aspirin reduced the risk of death from cancer by 20% across the population.  There are several large studies in the works to determine the risks vs. benefits of recommending aspirin therapy to everyone.[ref]

Aspirin is a blood thinner, so frequent use includes bleeding risks.  This seems to be the main argument against recommending aspirin as a cancer prevention method.

It turns out that genetics plays a role in whether aspirin reduces the risk of colon cancer for an individual.

So how does aspirin affect colon cancer?  
Cyclooxygenase (COX) is an enzyme involved in inflammatory responses.  It is also called prostaglandin-endoperoxide synthase (PTGS) and causes the formation of prostaglandins.  The problem with COX is that sometimes the inflammatory process doesn’t turn off when it is supposed to.

COX inhibitors decrease inflammation and thus the pain associated with it. Aspirin is a COX inhibitor, along with other NSAID pain relievers.  Other natural COX inhibitors include Vitamin D, St. John’s Wort, and fish oil.

Specific COX-2 only inhibitors, such as Vioxx, have been found to increase the risk of cardiovascular events.  (Vioxx was taken off the market in 2004 due to increased risk of heart attacks and strokes.)

Aspirin, along with most other over-the-counter NSAID’s, is both a COX-1 and COX-2 inhibitors.

Some cancer tumors express increased levels of COX, thus aspirin use could help reduce the risk of some cancer types.

Variants involved with aspirin and a reduced risk of colon cancer:

rs6983267 (T is the minor allele)

  • According to a 2013 study, those with the T allele benefitted from aspirin in the prevention of colon cancer.  Those with a T allele who were taking two or more regular aspirin in a week had their risk cut by 40 – 50%. [ref]
  • The T allele also reduces the overall risk of colon cancer [ref]
Check your 23andMe results for rs6983267 (v.4, v.5):

  • TT: reduced risk of colon cancer with regular aspirin use[ref]
  • GT: reduced risk of colon cancer with regular aspirin use
  • GG: no reduced risk of colon cancer with aspirin

rs7903146 (T is the minor allele, TCFL2 gene)

  • “Among individuals who reported recent use of aspirin/NSAIDs, the T allele reduced risk of colon cancer (OR, 0.78; 95% CI, 0.62-0.98) in a dose-response fashion” [ref]
Check your 23andMe results for rs7903146 (v.4, v.5):

  • TT: some reduction in risk of colon cancer with regular aspirin use[ref]
  • CT: some reduction in risk of colon cancer with regular aspirin use
  • CC: no reduced risk of colon cancer with aspirin

Other variants (not tested by 23andMe) also can lead to decreased colon cancer risks with aspirin.

Again, talk with your doctor and do your research on this before starting an aspirin regimen.  

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