Can drugs prevent colorectal cancer? An easy-to-understand explanation of the current state of chemoprevention
*This article is based on medical information, but it is not intended for diagnosis or treatment. Please be sure to consult your doctor regarding the use of any medication.
What is "chemoprevention"?
**Chemoprevention** is an approach that attempts to prevent the development of cancer itself using drugs or specific substances.
In the case of colorectal cancer, research is being conducted worldwide based on the idea that "if the development or recurrence of adenomas (polyps) can be suppressed with medication, the progression to cancer might also be prevented."
However, at this time, there is no drug that has been proven to reliably prevent the development of colorectal cancer.
On the other hand, there are several drugs that have been shown to be effective in suppressing the recurrence and growth of adenomas.
Research results targeting general patients
🟦 Celecoxib (COX-2 inhibitor)
In a randomized controlled trial comparing celecoxib (400 mg/day) with a placebo, the adenoma positivity rate after 3 years was 33.6% in the celecoxib group and 49.3% in the placebo group, indicating that the development of adenomas was significantly suppressed. An effect of reducing adenoma size has also been confirmed.
Note that the incidence of cardiovascular events (myocardial infarction, stroke, etc.) was 2.5% in the celecoxib group and 1.9% in the placebo group, with no significant difference.
🟦 Aspirin
A meta-analysis (integrated analysis) of multiple comparative trials showed that the incidence of adenomas was significantly lower in the aspirin-administered group.
⚠️ However, a prospective study in Japan has yielded results that require caution.
✅ In non-smokers, the adenoma incidence rate was significantly reduced (odds ratio 0.37)
❌ In smokers, the adenoma incidence rate was significantly increased (odds ratio 3.45)
The effect of aspirin may vary significantly depending on whether or not one smokes.
🟦 Calcium supplements (calcium carbonate)
In a comparative trial where calcium carbonate (1,200 mg/day) was administered for 4 years, there was no significant difference in the overall incidence of adenomas. However, the development of high-grade adenomas (tubulovillous adenoma, villous adenoma, high-grade dysplasia, invasive cancer) was significantly suppressed (relative risk 0.65).
🟦 Metformin (diabetes medication)
In a clinical trial targeting patients with a history of colorectal adenomas, the administration of metformin (250 mg/day) for one year significantly reduced the adenoma positivity rate in the active drug group (relative risk 0.6).
🟦 Substances for which no effect was confirmed
For the following drugs and ingredients, no effect in suppressing the development or recurrence of adenomas was confirmed.
❌ Folic acid
❌ Antihistamines (H1/H2 receptor antagonists)
❌ Vitamin D alone, calcium alone, or a combination of both
Research results targeting patients with colorectal adenomatosis (FAP)
Familial adenomatous polyposis (FAP) is a genetic disorder in which countless polyps form in the large intestine. Research targeting these patients has yielded the following results.
🟦 Celecoxib (400mg)
The number of adenomas decreased by 28%, and their size shrank by 30.7% (both statistically significant)
🟦 NSAIDs (non-steroidal anti-inflammatory drugs) in general
Meta-analysis shows the number of adenomas decreased by 11.9–44% in the NSAID group (significantly higher than the 4.5–10% in the placebo group)
🟦 EPA-FFA (eicosapentaenoic acid)
For adenomas in the remaining rectum, the number of adenomas decreased by 22.4% and the size shrank by 29.8% significantly
🗒️ Summary of research results
Celecoxib
Target: General population/Adenomatosis
Effect: Suppression of adenoma development/recurrence
Note: Consideration for cardiovascular risk is necessary
Aspirin
Target: General population
Effect: Suppression of adenoma development (non-smokers)
Note: Potential for adverse effects in smokers
Calcium supplements
Target: General population
Effect: Suppression of high-grade adenomas
Note: Effect on all adenomas is limited
EPA-FFA
Target: Adenomatosis
Effect: Reduction in number/size of adenomas
Note: Indicated for adenomatosis
Metformin
Target: History of adenomas
Effect: Reduction in adenoma positivity rate
Note: Diabetes medication
Important points
⚠️ All of the above studies demonstrate preventive effects on adenomas (polyps). There are no reports yet that they prevent the development of colorectal cancer itself.
Additionally, these drugs each have side effects and contraindications (cases where they should not be used). Avoid taking them on your own judgment for prevention, and be sure to consult your doctor.
Summary
At present, there is no drug that can reliably prevent the development of colorectal cancer, but celecoxib, aspirin, calcium supplements, and metformin have shown effects in suppressing the development or recurrence of adenomas. In particular, for patients with colorectal adenomatosis, the suppressive effects of celecoxib and EPA-FFA on adenomas have been demonstrated.
It is hoped that more reliable chemoprevention methods will be established through future research.
※ This article is intended to provide general medical information and does not constitute individual diagnosis or treatment. Please be sure to consult your attending physician regarding the use of any medication.