The rationale was that we know that aspirin confers some chemo-preventive benefits for certain malignancies, in particular colorectal cancer and some gastrointestinal malignancies the risk of incidence and death from those cancers is decreased with regular aspirin use. The effect of aspirin on prostate cancer is less clear, there are multiple observational studies that suggest aspirin may decrease the risk of advanced prostate cancer. So that’s the rationale – advanced prostate cancer is often defined as a composite of locally advanced or metastatic disease, so we really wanted to separate that out and look specifically at lethal disease.

So how many patients did you look at?

The Physicians’ Health Study enrolled over 22,000 male physicians beginning in 1982.

And what was the methodology?

This is a large cohort study, longitudinal cohort study, where these male physicians report their use of aspirin on an annual basis. It was initially designed as a randomised controlled trial to assess the impact of aspirin and beta carotene on cancer and myocardial infarction. The randomised aspirin component was stopped after five years when there was a clear benefit in terms of decreasing the risk of MI. So ever since that time it has been a cohort study and we’re regularly assessing detailed aspirin exposures on an annual basis.

Can you give me some results of what you’ve found so far?

Sure. Among the 22,000 participants after 27 years of follow-up we have over 3,100 cases of prostate cancer and of those 403 were lethal prostate cancer, so that was defined as metastases or death. We found that participants who used aspirin regularly, and that was defined as more than three tablets per week on average over the past year, had a decreased risk of developing lethal prostate cancer, a 24% decreased multi-variant adjusted risk. There was no effect on the incidence of overall prostate cancer or even of high risk prostate cancers. So we hypothesised that aspirin may not be preventing prostate cancer in the first place but be inhibiting its progression to lethality. So we did test that and did a survival analysis and found that aspirin use, regular aspirin use after diagnosis of prostate cancer, decreased the risk of prostate cancer death by 39% whereas pre-diagnostic regular aspirin use did not confer any measurable benefit.

So what would be the summary message coming out of this research?

I would say that that this study adds to the evidence that regular aspirin use probably decreases the risk of lethal prostate cancer, again not necessarily by preventing prostate cancer pathogenesis but by inhibiting its progression to metastases.

So there’s obviously evidence in colorectal as well? Would you yourself, when you get to a certain age, start taking preventative aspirin do you think?

I would recommend that potential aspirin users speak to their family physician. I think that there are obviously a lot of benefits in terms of not just cancer prevention but prevention of cardiovascular disease and stroke. It’s important for people to remember that although it’s an over the counter medication there are serious potential risks. So to make that decision I think you’d have to have a full discussion with your family physician going over the potential benefits and the risks.