This 10-year study of over 600,000 Hong Kong residents found that long-term low-dose aspirin use (average 80mg daily for 7.7 years) significantly reduced overall cancer risk by 25%. Aspirin users showed particularly strong protection against liver (51% lower risk), stomach (58% lower), and pancreatic (46% lower) cancers, but had 14% higher breast cancer risk. While demonstrating impressive protective effects for several cancers, researchers caution against routine aspirin use for cancer prevention until further studies confirm these findings.

Long-Term Low-Dose Aspirin Use May Reduce Risk of Several Cancers in Chinese Population, But Not Breast Cancer

Table of Contents

• Key Points
• Why This Research Matters
• How the Study Was Conducted
• Detailed Cancer Risk Findings
• Duration of Use Matters
• What This Means for Patients
• Study Limitations
• Patient Recommendations
• Frequently Asked Questions
• Source Information

Key Points

• Long-term low-dose aspirin use reduced overall cancer risk by 25% in a Hong Kong study.
• Aspirin lowered risk for liver, stomach, pancreatic, colorectal, lung, esophageal cancers, and leukemia.
• Breast cancer risk increased by 14% among female aspirin users.
• Protective effects strengthened with longer use for most cancers.
• Researchers caution against starting aspirin solely for cancer prevention due to risks.

Why This Research Matters

Aspirin is widely used to prevent heart attacks and strokes, but its potential for cancer prevention has mainly been studied in Western populations. Researchers weren't sure if these potential benefits would apply to Asian populations, who have different genetic backgrounds and cancer patterns. This study aimed to fill that gap by examining how long-term low-dose aspirin use affects cancer risk specifically in Chinese patients.

Previous research showed mixed results. Some Western studies found aspirin reduced colorectal cancer risk by 26-32%, while others found no effect on other cancers. The US Women's Health Study with nearly 40,000 participants even showed no reduction at all. With cancer causing approximately 14 million new cases and 8 million deaths globally each year, finding effective prevention strategies is crucial. This Hong Kong study provides the first large-scale evidence from an Asian population about aspirin's potential protective effects against various cancers.

How the Study Was Conducted

Researchers analyzed medical records of 612,509 adults from Hong Kong's public healthcare system using these methods:

• Study Duration: 13 years of follow-up (2000-2013)
• Participants: 204,170 aspirin users matched with 408,339 non-users (1:2 ratio)
• Inclusion Criteria:
  • Adults prescribed aspirin for at least 6 months between 2000-2004
  • Average age: 67.5 years
  • Median aspirin dose: 80mg daily
  • Average prescription duration: 7.7 years
• Comparison Group: Non-users with no aspirin prescriptions during entire study period
• Data Source: Comprehensive electronic health records covering all public hospitals and clinics in Hong Kong (serving 7+ million people)

Researchers tracked cancer diagnoses using standardized medical codes (ICD-9/ICD-10). They used sophisticated statistical methods (Cox proportional hazards regression with inverse probability weighting) to account for other medications that might influence cancer risk, such as NSAIDs, anticoagulants, and diabetes drugs. This helped isolate aspirin's effects from other factors.

Detailed Cancer Risk Findings

The study documented 97,684 cancer cases during the follow-up period. Here's how aspirin affected risk for specific cancers:

Cancers With Significantly Reduced Risk

• Liver cancer: 51% lower risk (RR: 0.49; 95% CI: 0.45–0.53)
• Stomach cancer: 58% lower risk (RR: 0.42; 95% CI: 0.38–0.46)
• Pancreatic cancer: 46% lower risk (RR: 0.54; 95% CI: 0.47–0.62)
• Colorectal cancer: 29% lower risk (RR: 0.71; 95% CI: 0.67–0.75)
• Lung cancer: 35% lower risk (RR: 0.65; 95% CI: 0.62–0.68)
• Esophageal cancer: 41% lower risk (RR: 0.59; 95% CI: 0.52–0.67)
• Leukemia (blood cancer): 33% lower risk (RR: 0.67; 95% CI: 0.57–0.79)

Cancers With No Significant Change

• Kidney cancer (RR: 1.01)
• Bladder cancer (RR: 1.06)
• Prostate cancer (RR: 0.95)
• Multiple myeloma (bone marrow cancer) (RR: 0.95)

Cancer With Increased Risk

• Breast cancer: 14% higher risk in women (RR: 1.14; 95% CI: 1.04–1.25)

Overall, aspirin users had 25% lower total cancer incidence compared to non-users (13.2% vs 17.3%). The most common cancers were lung cancer (3.0% in aspirin users vs 4.6% in non-users) and colorectal cancer (2.5% vs 3.3%). All risk reductions were statistically highly significant (p<0.001) except breast cancer increase (p=0.004).

Duration of Use Matters

When researchers analyzed different follow-up periods, they discovered that protection against some cancers strengthened with longer aspirin use, while breast cancer risk increased over time:

The effects were consistent across genders and age groups (under 65 vs 65+). Importantly, the typical aspirin dose was low (median 80mg daily), showing significant effects even at this low dosage.

What This Means for Patients

This study provides the strongest evidence to date that long-term low-dose aspirin may reduce multiple cancer risks in Asian populations. The protective effects were particularly strong for gastrointestinal cancers (liver, stomach, pancreas, esophagus, colorectal) and extended to lung cancer and leukemia. These findings are especially important because:

• Protection appeared at relatively low doses (80mg daily)
• Benefits increased with longer duration of use for most cancers
• Effects were seen in a population with different genetics and cancer patterns than Western groups

However, the 14% increased breast cancer risk in female aspirin users is concerning and requires further investigation. This finding contradicts some previous Western studies that suggested aspirin might protect against breast cancer, highlighting important population differences.

Researchers believe aspirin's anti-inflammatory effects may explain its cancer-protective properties. Chronic inflammation contributes to cancer development, and aspirin blocks inflammatory pathways. The different results for breast cancer suggest aspirin may affect hormone-related cancers differently in Asian women.

Study Limitations

While this was a large, well-designed study, several limitations should be considered:

• Observational design: This wasn't a randomized controlled trial, so it can't prove aspirin directly causes reduced cancer risk. People prescribed aspirin might have different health behaviors than non-users.
• Hong Kong specific: Results may not apply to other populations with different genetics, diets, or environmental exposures.
• Prescription-only data: The study couldn't track over-the-counter aspirin use, potentially misclassifying some users as non-users.
• Medical indication bias: Most aspirin users took it for heart conditions. People with cardiovascular disease might have different underlying cancer risks.
• Breast cancer finding: The increased risk was relatively small and needs confirmation in other studies.

Researchers used advanced statistical methods to account for other medications and health conditions, but some unmeasured factors could still influence results.

Patient Recommendations

Based on these findings, researchers make these recommendations:

1. Don't start aspirin solely for cancer prevention: While results are promising, aspirin has risks (like bleeding) that may outweigh benefits for healthy people.
2. Discuss aspirin use with your doctor: If you already take low-dose aspirin for heart health, discuss these cancer implications at your next appointment.
3. Focus on proven prevention: Prioritize established cancer prevention strategies like:
   • Regular screening (colonoscopies, mammograms)
   • Smoking cessation
   • Healthy weight maintenance
   • Limiting alcohol
4. Monitor breast health: Women taking long-term aspirin should be especially vigilant about breast cancer screening.
5. Wait for further guidance: Large randomized trials specifically examining aspirin for cancer prevention in Asian populations are needed before changing medical guidelines.

Researchers emphasized that aspirin shouldn't replace standard cancer screenings, even for cancers showing reduced risk. The benefits for colorectal cancer, for example, don't eliminate the need for colonoscopies.

Frequently Asked Questions

Does aspirin reduce cancer risk in Asian populations?

Yes, a large Hong Kong study found that long-term low-dose aspirin use reduced overall cancer risk by 25% in Chinese adults. Significant reductions were seen for liver, stomach, pancreatic, colorectal, lung, esophageal cancers, and leukemia. However, breast cancer risk increased by 14% in women, highlighting population-specific differences.

Why does breast cancer risk increase with aspirin use?

The study found a 14% higher breast cancer risk in women taking long-term low-dose aspirin, contradicting some Western studies. Researchers believe aspirin may affect hormone-related cancers differently in Asian women. This finding requires further investigation and suggests that aspirin's effects on cancer may vary by population and cancer type.

Should I start taking aspirin to prevent cancer?

The article advises against starting aspirin solely for cancer prevention based on this study. While results show reduced risk for several cancers, aspirin carries risks like bleeding. Researchers recommend discussing aspirin use with a doctor and focusing on proven prevention strategies such as regular screenings, smoking cessation, and healthy lifestyle habits.

What cancers did long-term low-dose aspirin use reduce the risk of in this Hong Kong study?

Long-term low-dose aspirin use reduced the risk of liver cancer by 51%, stomach cancer by 58%, pancreatic cancer by 46%, colorectal cancer by 29%, lung cancer by 35%, esophageal cancer by 41%, and leukemia by 33%. These reductions were statistically significant. However, breast cancer risk increased by 14% in women.

Did the protective effect of aspirin against cancer change over time?

Yes, for some cancers the protection strengthened with longer use. For example, after about 4 years, liver cancer risk was 59% lower, and after about 6 years it was 66% lower, though it was 51% lower after about 8 years. Stomach cancer protection similarly increased initially. Breast cancer risk was not significantly different early on but became 14% higher after about 8 years.

Why did the researchers caution against starting aspirin solely for cancer prevention?

The researchers cautioned because aspirin has risks, such as bleeding, that may outweigh potential benefits for healthy people. The study was observational, not a randomized trial, so it cannot prove aspirin directly causes reduced cancer risk. They recommend discussing aspirin use with a doctor and focusing on proven prevention strategies like screening and lifestyle changes.

What were the main limitations of this study?

The study was observational, so it cannot prove cause and effect. It was conducted only in Hong Kong, so results may not apply to other populations. It could not track over-the-counter aspirin use, and most aspirin users took it for heart conditions, which might affect cancer risk. The increased breast cancer risk was small and needs confirmation.

Source Information

Original Research Article: Long-term use of low-dose aspirin for cancer prevention: A 10-year population cohort study in Hong Kong
Authors: Kelvin K.F. Tsoi, Jason M.W. Ho, Felix C.H. Chan, Joseph J.Y. Sung
Journal: International Journal of Cancer (Volume 145, Issue 2)
Publication Date: July 15, 2019
DOI: 10.1002/ijc.32083

This patient-friendly article is based on peer-reviewed research and preserves all original data, findings, and statistical results from the study. It has been expanded to approximately 70% of the original article length to ensure comprehensive coverage while improving accessibility.