Already hailed for its value in lowering risk for heart attacks and stroke, this month’s media buzz around aspirin posits the pill as a promising means for one day preventing and slowing the spread of malignant tumors.
But don’t run to the pharmacy just yet, warns cancer epidemiologist Dr. Susan Fisher – there’s a lot we’ve yet to learn. For the panoramic perspective on the issue, read on.
Scripts: New research out this month suggests that taking aspirin daily may substantially cut risk for the development and spread of many cancers. Has this phenomenon been long-suspected?
Fisher: Frankly, to scientists, it’s not a brand new concept. For years, researchers have studied the benefits of aspirin for preventing cardiovascular disease (e.g., heart attacks and strokes), and these data, rather fortuitously, also have suggested that those taking aspirin subsequently seem to be at lower risk for many types of cancer. Even so, it’s crucial to note that results have been mixed; some of the research has not shown a benefit, and other studies have required a higher daily dose of aspirin, which in turn increases the risk of side effects such as gastrointestinal bleeding or hemorrhagic stroke.
Scripts: To the average reader, these study numbers seem pretty promising, though – especially for colon cancer. What can we make of this?
Fisher: Granted, the results are rather intriguing – for participants adhering to a low-dose aspirin regimen, they show a 12 percent reduction in cancer incidence after three years of the therapy, and a 15 percent reduction in cancer death after three to five years. What’s even more interesting, the studies also showed that persons taking aspirin had a reduced risk of cancer metastasis (disease spread to other organs), which could in part account for the decreased risk of death.
Still, context is really important. While these new findings included five prevention studies completed in the United Kingdom, they specifically excluded two U.S. prevention studies that showed no reduction in colorectal cancer incidence, overall cancer incidence, or cancer mortality with every-other-day aspirin therapy. It’s also important to note that while the numbers seem striking, the “relative reduction” remains small when considering aspirin therapy for the general population who has no increased risk of cancer. Let me explain it this way: To researchers, the concept of “number needed to treat” is an important measure when thinking about prevention. Based on these new data, approximately 625 people would need to take aspirin for a year in order to prevent the occurrence of cancer in one person – and over 1,000 people would need to take aspirin daily to prevent one cancer death. Certainly, for that one person, taking aspirin may be considered a low-risk preventive measure – but for the many others who were unlikely to develop cancer anyway, the risk of bleeding due to regular aspirin therapy is concerning.
Unquestionably , these are provocative results. But there’s substantial room for misinterpretation of the direct benefit of aspirin, and more research much be done before we recommend that the general public begin to take aspirin as if it were a daily vitamin.
Scripts: So, in your mind, it’s far more likely that, one day, aspirin could be reserved as a therapeutic approach for patients diagnosed with certain cancers (like colon cancer) or who are at special risk for developing them?
Fisher: Yes, it’s certainly possible – but again, this decision would have to be reached between a patient and their personal physician.
That said, I can’t help but emphasize that the safest, best-proven method for preventing colon cancer is a colonoscopy – a routine exam to check for and remove pre-cancerous growths called polyps. The same goes for other recommended cancer tests like mammograms, pap smears, and, for some men at high-risk, prostate screenings.
Scripts: That makes sense. Do we know why aspirin seems to help fend off cancer/slow cancer’s spread?
Fisher: We don’t know precisely why aspirin might reduce cancer risk, but we do know that aspirin works to inhibit the function of blood cells called “platelets, which are important for clotting. (This is why aspirin tends to decrease the risk of blood clots, but on the other side also causes excessive bleeding is some people.) Since platelets have a confirmed role in cancer growth and spread, it may be that fewer working platelets translates into decreased tumor growth and metastasis – a finding already shown in mice, but not directly in humans.
Scripts: Is there anything else about the study that’s important to bear in mind when interpreting this news?
Fisher: Yes. While the idea that aspirin could cut cancer risk is biologically plausible – and exciting – we should wait on drawing conclusions and formulating official recommendations until seeing the long-term results of two U.S. studies (previously mentioned). Again, these were specifically designed to examine cancer endpoints with aspirin treatment.
It’s also important to be aware that, although the media are suggesting that there were three separate studies released this month, the same study group (same lead investigator) produced all of them. It’s really important that other investigators in turn confirm these findings. What’s more, it’s important to appreciate that these studies did not manipulate newly gathered data, but are analyses of data previously collected for other purposes (e.g., cardiac research studies). Sometimes, these sorts of analyses can be limited (and even biased), since they were not originally designed to answer the specific new questions being addressed.
As professor and chair of URMC’s Department of Community and Preventive Medicine, Dr. Fisher’s research focuses on the investigation of strategies to improve the primary prevention and early detection of cancer in the community. She’s been involved in the development and conduct of several multi-institutional clinical trials.
You can learn more about clinical trials underway at URMC by clicking here.