An aspirin a day keeps the cancer away
More evidence is accumulating that aspirin can reduce the risk of being stricken with cancer, suffering from metastatic cancer, and dying from cancer. Many individuals now are on an aspirin regimen not only to reduce the risk of a cardiovascular event but also to reduce the risk of cancer. Three new studies were published online on March 21 in the journals The Lancet and The Lancet Oncology, which support this premise. The lead author of all three studies was Peter M. Rothwell, MD, PhD, professor of clinical neurology at the University of Oxford, United Kingdom.
In the first study, published in The Lancet Oncology, the researchers noted that long-term follow-up of randomized trials of aspirin in prevention of cardiovascular events reported that daily aspirin reduced the incidence of colorectal cancer and several other cancers; in addition, they reported a reduced incidence of metastases. However, they noted that these studies did not have enough statistical significance to establish the effects of an aspirin regimen on less common cancers or on cancers in women. Therefore, they compared the effects of aspirin on risk and outcome of cancer in observational studies versus randomized trials.
The researchers conducted a systematic review of studies published from 1950 to 2011, which reported associations between aspirin use and risk or outcome of cancer. A total of 17 studies reported a reduced risk of colorectal cancer. Similar risk reductions were found in risks of esophageal, gastric, biliary, and breast cancers. A review of 41 randomized trials found that the estimates of effect of aspirin on individual cancers in case control studies highly correlated with those in randomized trials, with the greatest effects on risk of gastrointestinal cancers. Although the researchers found fewer observational studies, which separated out the stage of cancer at diagnosis, regular use of aspirin was associated with a decrease in cancers with distant metastases in five studies.
In the second study, published in The Lancet, the researchers noted that daily aspirin reduces the long-term risk of death due to cancer. However, they stated that the short-term effect of an aspirin regimen on cancer prevention was less certain, especially in women. Thus, they studied cancer deaths in all trials of daily aspirin compared to a control group as well as the time course of effects of low-dose aspirin on cancer incidence and other outcomes.
The investigators reviewed 51 trials, comprised of 77,549 subjects. A total of 562 deaths occurred among patients on an aspirin regimen, compared to 664 in control groups, particularly among those who took aspirin for five years or more. In trials evaluating primary prevention of cancer, the reduction in non-vascular deaths accounted for 87 (91%) of 96 deaths prevented. In six trials (35,535 subjects) of daily low-dose aspirin for primary prevention, aspirin reduced the cancer incidence from three years onwards (aspirin: 324 deaths; control: 421 deaths). When separated by gender, 132 deaths occurred among women taking aspirin, compared to 176 controls. For men, 192 deaths occurred among those taking aspirin vs. 245 in the control groups. The study authors also noted that the reduced risk of major cardiovascular events (i.e., a heart attack or stroke) for those on an aspirin regimen was initially offset by an increased risk of major bleeding; however, the effects of either cancer or bleeding diminished with increasing follow-up, leaving only the reduced risk of cancer from three years onwards. Deaths from a major extracranial (not within the skull) bleeding episode were also lower on the subjects who took aspirin (8/203 vs. 15/132).
The authors concluded that in addition to a reduction in the long-term risk of cancer death, the following benefits of a long-term aspirin regimen: short-term reductions in cancer incidence and mortality; and a decreased risk of a major extracranial bleed. They noted that their study added additional benefits for daily aspirin as a cancer preventative.
In the third study, also published in The Lancet, the researchers examined the risk of distant metastases in patients who developed cancer during trials of daily aspirin compared tp control groups. They reviewed five large randomized trials (17,285 total subjects) of a daily aspirin regimen (75 mg or more daily) versus control groups for the prevention of cardiovascular events in the United Kingdom. They found that 987 new cancers were diagnosed during an average follow-up of 6.5 years. Compared to controls, the subjects on an aspirin regimen had a reduced risk of distant metastases, adenocarcinoma, and other solid cancers. Aspirin reduced the risk of adenocarcinoma with metastases both at initial diagnosis and at subsequent follow-up in patients without metastases initially, particularly in patients with colorectal cancer and in patients who remained taking aspirin up to or following diagnosis. They noted that aspirin reduced death due to cancer in patients who developed adenocarcinoma, particularly in those without metastases at diagnosis. Aspirin reduced the overall risk of a fatal adenocarcinoma; however, it did not reduce the risk of other fatal cancers. These effects were independent of age and sex; however, the absolute benefit was greatest in smokers. In addition, they found that a low-dose, slow-release formulation of aspirin designed was as effective as higher doses. The importance of this finding is that the aforementioned formulation has a lower risk of bleeding.
Take home message:
Although aspirin is readily available over the counter, remember that it is a drug and all drugs have a risk of side-effects. For individuals with a history (or family history) of heart disease, blood clots, or colon cancer, the benefits of aspirin outweigh the risks for most. In addition, if you are on an aspirin regimen or are considering beginning one, it is prudent to discuss the pros and cons with a healthcare professional.