By Monique Biryiana

A systematic review published in PLOS ONE  suggests that the adjuvant administration of low-dose aspirin to patients with colorectal, breast and prostate cancer may be associated with a reduced risk of metastases and increased survival.

Only a few studies have previously reported a reduction in the metastatic spread of cancer after aspirin treatment, however these have focused on a using randomised controlled trial design with a small number of participants. The Add-aspirin clinical trial (Coyle et al., 2016) is currently in its third phase, however data from this study may not be readily available for another 10 -15 years. Therefore, current research into this association has been restricted to the use of observational studies only.

This review sets out to identify whether there is a significant benefit for low-dose aspirin administration in cancer patients and whether this effect is specific to colorectal, breast or prostate cancer.

By using a meta-analysis approach, this study combines the results from a previous systematic review collected in April 2015 with further results collected by the authors in August 2017.

A total of 869 papers containing over 120,000 patients were identified using a literature search from April 2015 to August 2017, however only 71 of these studies were progressed to the meta-analysis stage.

29 studies identified the association between colorectal cancer mortality and post-diagnostic aspirin and a pooled hazard ratio (HR) of 0.72 (95% CI 0.64 – 0.80) was calculated.

Additionally, 14 studies investigated the association between aspirin and breast cancer mortality and an overall HR of 0.69 (0.52 – 0.90) was presented.

Furthermore, 16 studies reported an association between aspirin and prostate cancer mortality and a pooled HR of 0.87 was also calculated (95% CI 0.73 – 1.05) from these papers.

A reduction in the metastatic spread was also observed, as a pooled HR of 0.31 (95% CI 0.18 - 0.54) was calculated in 4 studies.

Overall, the HRs calculated for the association between aspirin and cancer mortality revealed a smaller risk of mortality for colorectal, breast and prostate cancer patients.

However, there are concerns about possible adverse effects, including the increased risk of bleeding that these patients may experience whilst taking aspirin. Other variables that may affect the effectiveness of the drug include age, body weight and the dose of aspirin that is administered. Increased heterogeneity between studies and the risk of bias also raises concerns in regard to the validity of these results. 

Nonetheless, the evidence presented in this study warrants further discussions about the therapeutic benefit that low-dose aspirin could provide for certain cancers.

References:

Coyle C, Cafferty FH, Rowley S, MacKenzie M, Berkman L, Gupta S, et al. (2016) Add-aspirin: a phase III, double-blind, placebo controlled, randomised trial assessing the effects of aspirin on disease recurrence and survival after primary therapy in common non-metastatic solid tumours. Contemporary Clin Trials 51: 56–64.
DOI: 10.1016/j.cct.2016.10.004

Elwood, P., Pickering, J., Morgan, G., Galante, J., Weightman, A., Morris, D., Longley, M., Mason, M., Adams, R., Dolwani, S., Chia W. K., J. and Lanas, A. (2018). Systematic review update of observational studies further supports aspirin role in cancer treatment: Time to share evidence and decision-making with patients?. PLOS ONE, 13(9), p.e0203957.
DOI: 10.1371/journal.pone.0203957