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Can aspirin reduce breast cancer risk?

Friday 7 March 2008

“Will taking an aspirin a day cut the risk of breast cancer?” asks the Daily Mail . The newspaper reports that an expert analysis of 21 studies has found that “non-steroidal anti-inflammatory drugs [NSAIDs] – the class of common painkiller which also includes ibuprofen – could ward off the disease.”

The Independent also reports on the study saying that aspirin can reduce the risk of breast cancer by about 20%, while The Daily Telegraph says that NSAIDs could also be used to treat women already diagnosed with breast cancer “by helping hormone treatments to work to their maximum effectiveness”.

The source of these stories is a non-systematic review that summarises current literature on the effects of NSAIDs on the risk of developing breast cancer, and in its treatment. However, studies on the prevention of breast cancer have, to date, been observational studies, and in order to come to a firm conclusion, a randomised controlled trial is needed.

In light of these limitations, women should not start taking aspirin to reduce their risk of breast cancer. As mentioned in the newspapers, these drugs do have side effects, including stomach ulcers and heart disease for some NSAIDs. Author Professor Ian Fentimann says, “We are not advocating that women take these non-prescription drugs routinely until the benefits and risks are clearer.”

Where did the story come from?

Mr Agrawal and Professor Ian Fentiman from the Hedley Atkins Breast Unit at Guy’s Hospital wrote this literature review. The review received no specific funding. The review was published in the peer-reviewed: International Journal of Clinical Practice .

What kind of scientific study was this?

This was a non-systematic review of the literature about the relationship between non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen and aspirin, and breast cancer.

The researchers searched the MEDLINE literature database for relevant studies addressing the use of NSAIDs for the prevention or treatment of breast cancer, and the possible biological mechanisms by which they might have an effect. No further criteria for selecting studies for inclusion were described. The authors then wrote a discussion of the results of the studies they had identified.

What were the results of the study?

The authors discussed how NSAIDs might biologically affect breast cancer development, and say that a study in animals has shown that they can reduce breast tumours. They describe a study published in 2001 that pooled the results of six cohort studies and eight case-control studies and which found an 18% reduction in the risk of developing breast cancer with NSAIDs (mostly aspirin). This study concluded that NSAIDs “might be associated with a small decrease in the risk of developing breast cancer”.

A subsequent study published in 2003 pooled the results of 13 cohort studies and 34 case-control studies, and also found a similar reduction in the risk of breast cancer with NSAIDs. However, a large and good quality Danish study published in the same year found that NSAIDs other than aspirin did not reduce the risk of breast cancer.

The authors describe later case-control and cohort studies, with conflicting findings, including the suggestion that aspirin reduced breast cancer risk, that the evidence supporting an effect of other NSAIDs is conflicting, and that use of high doses of NSAIDs, including aspirin, might increase the risk of breast cancer. However, the authors reported that studies had yet to determine what the best type and dose of NSAID for breast cancer prevention, and for how long it should be used.

The authors also reported on studies that looked at the effects of NSAIDs in women who already had breast cancer. These included two studies that looked at biochemical changes in response to NSAIDs. One study found no reduction in death from breast cancer in women who used NSAIDs after they were diagnosed, although overall deaths were reduced.

The authors also discuss several studies that looked at the use of the NSAID celecoxib in combination with exemestane (a hormone therapy) in women with breast cancer. Celecoxib is a COX-2 inhibitor, and was associated with cardiovascular adverse events in two of these trials, and also another previous cancer prevention trial in people with colon polyps. Because of this, the authors questioned whether celecoxib would be appropriate for use in further studies.

What interpretations did the researchers draw from these results?

The researchers concluded that “NSAIDs may reduce breast cancer risk by 20%”, but that the ideal dosage, dose and length of time of NSAIDs that would be needed for the optimum effect is not known.

They also say that it is not known whether such an intervention would be feasible in an at risk population. Finally, they suggest that there “may be a role for NSAIDs in combination" with other treatments for breast cancer.

What does the NHS Knowledge Service make of this study?

This study did not report a systematic method for identifying and assessing the quality of the studies that were included; therefore, it is difficult to know whether all relevant studies have been included and whether the quality of the included studies has been fully assessed. Although the meta analyses the authors describe do suggest that there might be some benefits of NSAIDs, particularly low dose aspirin, an updated systematic review and meta analysis including the newer studies described is needed. It must also be noted that some studies found that higher doses of NSAIDS increased the risk of breast cancer.

Whether NSAIDs have a role in the treatment of breast cancer beyond their role as painkillers remains to be seen. In order to truly determine the benefits of aspirin or the NSAIDs in the prevention or treatment of breast cancer, a randomised controlled trial is needed. People should also be aware of the risks associated with regular aspirin use, in particular stomach irritation and the potential for bleeding and ulcers in the stomach. In light of these limitations, women should not start taking aspirin solely in order to reduce their risk of breast cancer.

Sir Muir Gray adds...

This needs more analysis, but it’s an important idea that merits further investigation.

Analysis by Bazian
Edited by NHS Website

Links to the science

Asano TK, McLeod RS.

Non steroidal anti-inflammatory drugs (NSAID) and aspirin for preventing colorectal adenomas and carcinomas.

Cochrane Database of Syst Rev 2004, Issue 1

Further reading McNicol E, Strassels SA, Goudas L, Lau J, Carr DB, et al.

NSAIDS or paracetamol, alone or combined with opioids, for cancer pain.

Cochrane Database of Syst Rev 2005, Issue 2

Agrawal A, Fentiman IS.

NSAIDs and breast cancer: a possible prevention and treatment strategy.

Int J Clin Pract 2008; 62:444–449