Aspirin’s Evolving Role in Cancer Prevention and Outcomes

Aspirin (Bayer), the century-old analgesic and antiplatelet agent, is generally known for its cardiovascular benefits. However, a growing body of evidence indicates that its effect could be broader, especially concerning cancer prevention and patients’ survival. While investigators continue to unravel observational and clinical data spanning several decades, clinicians and pharmacists are tasked with understanding the promise and limitations of aspirin in oncology care and cancer risk management.

Epidemiological Evidence: Aspirin and Long-Term Cancer Risk

Investigators of a rigorous 20-year cohort study, whose findings were published in the Journal of the National Cancer Institute, examined the association between long-term aspirin use and the risk of cancer of various types. Among the more than 1.9 million individuals who were monitored for a period of up to 20 years, regularly taking low-dose aspirin (75 mg, 150 mg) did not drastically reduce the overall risk of cancer; however, detailed analyses on specific locations of the body showed that risk ratios for the colon, rectum, esophagus, stomach, liver, pancreas, and other parts of the gastrointestinal tract, as well as systemic ones, decreased by 10% or more.¹

These findings are consistent with previous observational data showing that regular use of aspirin is associated with a lower colorectal cancer risk and a lower chance of disease recurrence, particularly among individuals at a high risk of colorectal cancer. This includes those with hereditary cancer syndromes such as Lynch syndrome.² In fact, daily treatment with aspirin in higher doses has been linked to a markedly lower risk of colorectal cancer in the long-term in patients with Lynch syndrome, with divergence in the risk usually appearing after a few years of use.³

Biological Mechanisms: Beyond Pain Relief

The potential anticancer effects of aspirin are based on various biological mechanisms, many of which are independent of the drug’s platelet aggregation and anti-inflammatory properties. The drug inhibits cyclooxygenase (COX) enzymes, mainly COX-2, in an irreversible manner, thereby reducing the production of prostaglandins, which are involved in tumor cell proliferation and new blood vessel formation.⁴

Data from preclinical and epidemiological studies have highlighted COX-2 overexpression in various cancers and have associated the drug’s downregulation with a decreased risk of tumor initiation and progression.⁵

Findings from new mechanistic studies indicate that aspirin may affect cancer metastasis by reducing platelet activation and suppressing mechanisms that allow circulating tumor cells to evade immune surveillance. It has been suggested that inhibiting platelet-released factors, such as thromboxane A2, could boost T-cell–mediated immune responses to cancer cells spreading, providing a reasonable explanation for the lower incidence of metastases.⁶

Clinical Implications: Survival and Recurrence

Besides its role in reducing cancer risk, aspirin has also been positioned as a beneficial agent for improving cancer outcomes after diagnosis, attracting substantial attention. Results from meta-analyses of observational studies have shown that aspirin use is consistently associated with better survival and reduced metastatic spread across a variety of cancers.⁷ These correlations could be the result of tumor-intrinsic effects as well as aspirin’s influence on the tumor microenvironment.

For patients with colorectal cancer, a growing body of evidence supports the use of daily low-dose aspirin not only to reduce the chance of relapse but also to enhance prolonged survival without the disease, particularly in tumors with certain molecular characteristics such as PIK3CA mutations. Data from some prospective cohort studies and secondary analyses of trials indicate that recurrence rates among aspirin users are up to 55% lower than among nonusers; however, randomized controlled trials are needed to verify these findings.⁸

Balancing Benefits and Risks

Despite compelling data, the use of aspirin as a universal cancer preventive agent remains a matter of debate. Findings from large, randomized trials, such as the ASPREE study (NCT01038583), showed no beneficial effect of low-dose aspirin on overall cancer incidence in older adults and even suggested that cancer-related mortality may have increased in some participants.⁹ These divergent outcomes reflect the heterogeneity of the evidence and underscore the necessity of individualized patient assessment.

Long-term aspirin use is known to have adverse effects, such as gastrointestinal bleeding and hemorrhagic stroke, which must be taken into consideration along with anticancer benefits, particularly in populations without compelling cardiovascular indications.

Conclusions and Future Directions

Aspirin’s role in cancer prevention and survival continues to evolve, supported by a mix of epidemiological, mechanistic, and clinical data. Long-term use appears to confer modest reductions in site-specific cancer risk and may improve outcomes for certain patients, particularly in colorectal cancer. Yet evidence remains inconsistent across cancer types and age groups. Clinicians should engage in shared decision-making with patients, considering individual risk factors, cancer history, and bleeding risks when contemplating aspirin therapy beyond cardiovascular indications. Future randomized trials and molecularly stratified research will be critical to clarifying aspirin’s role in cancer prevention and as an adjunctive therapy.

REFERENCES

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