How Cancer Ireland Evaluates Evidence

Cancer Ireland includes information from different types of evidence, ranging from systematic reviews and randomized controlled trials to observational studies, case reports, mechanistic research, and patient experience.

Not all evidence carries the same weight. A therapy may be biologically plausible, widely used, or supported by early research, but still lack strong clinical evidence showing that it improves outcomes in cancer patients.

This page explains how evidence is interpreted on this site.

Stronger for clinical decision-making:
– Systematic reviews and meta-analyses of good-quality human studies
– Randomized controlled trials
– Well-designed cohort and case-control studies

Useful but less definitive:
– Small clinical trials
– Case series and case reports
– Expert opinion and anecdotal evidence
– Mechanistic and preclinical evidence

Stronger Evidence

These forms of evidence are generally more useful for assessing whether a treatment, therapy, drug, supplement, or lifestyle intervention may improve clinical outcomes.

Systematic reviews and meta-analyses

Systematic reviews and meta-analyses combine findings from multiple studies. When they include high-quality studies with consistent results, they can provide some of the strongest evidence available.

However, a meta-analysis is only as reliable as the studies it includes. A meta-analysis of weak, biased, or highly varied studies may still produce uncertain conclusions.

Randomized controlled trials

Randomized controlled trials, or RCTs, are often considered the strongest individual study design for testing whether an intervention causes a clinical effect.

In an RCT, participants are assigned to different groups, usually an intervention group and a comparison or control group. This helps reduce bias and makes it easier to judge whether the intervention itself contributed to the result.

However, RCTs can still vary in quality. Small sample size, short follow-up, poor blinding, selective reporting, or inappropriate endpoints can weaken their conclusions.

Cohort and case-control studies

Cohort and case-control studies are observational studies. They can be valuable, especially when randomized trials are unavailable, impractical, or unethical.

These studies can show associations between an intervention or exposure and an outcome, such as recurrence, survival, side effects, or quality of life. However, they usually cannot prove cause and effect on their own, because the results may be influenced by confounding factors.

For example, people who take a supplement, exercise regularly, or follow a particular diet may also differ in other important ways from people who do not.

Weaker or Early-Stage Evidence

These forms of evidence can still be useful, but they are generally less able to prove that a therapy improves cancer outcomes in patients.

Case series and case reports

Case reports describe the experience of one patient. Case series describe a small group of patients.

These reports can be important for identifying unusual responses, possible benefits, side effects, or new hypotheses. However, they cannot reliably prove that a treatment caused the outcome, because there is usually no control group.

Expert opinion and anecdotal evidence

Expert opinion and patient anecdotes can sometimes highlight important clinical observations, especially when formal research is lacking.

However, anecdotal evidence is highly vulnerable to bias, coincidence, incomplete information, placebo effects, spontaneous improvement, and the influence of other treatments being used at the same time.

On this site, credible expert and anecdotal evidence is included where relevant, because it may benefit cancer patients – especially those with limited options.

Mechanistic and preclinical evidence

Mechanistic and preclinical evidence includes laboratory studies, cell studies, animal studies, and research into biological pathways.

This type of evidence can help explain why a therapy might work. For example, it may show effects on inflammation, angiogenesis, immune signalling, oxidative stress, apoptosis, metabolism, the microbiome, or treatment resistance.

However, effects seen in cells or animals do not always translate into meaningful benefit in human cancer patients. For that reason, mechanistic evidence is useful for biological plausibility, but it is not treated as clinical proof.

How Evidence Is Interpreted

Cancer Ireland does not treat all evidence as equal. When reviewing a therapy, the following questions matter:

• Has it been studied in humans?
• Has it been studied in cancer patients specifically?
• Was the outcome clinically meaningful, such as survival, recurrence, treatment response, side effects, or quality of life?
• Was the study randomized, observational, mechanistic, or anecdotal?
• Were the results replicated by independent researchers?
• Are there plausible safety concerns or interactions?
• Is the dose used in the study achievable and safe in real-world use?
• Was the product or intervention in the study the same as what patients can actually buy or access?

A therapy may be included on this site because it is scientifically interesting, biologically plausible, commonly used, low-cost, or supported by some level of evidence. Inclusion does not mean that the therapy has been proven to work.

Supplement quality, contamination risk, dose safety, and treatment interactions

Supplements are regulated differently from prescription drugs. In the United States, the FDA regulates dietary supplements under a different framework from drugs, and supplement products generally do not require FDA approval before being sold. In the European Union, EFSA states that food supplements are considered foodstuffs, and responsibility for product safety lies with the food business operator placing the product on the market.

This means supplement quality, purity, dosage accuracy, and contamination risk can vary between products. Supplements bought in shops or online may also differ from the specific products used in research studies. The NIH National Center for Complementary and Integrative Health notes that dietary supplements can interact with medicines, may pose risks in certain medical situations, and may differ in important ways from products tested in studies.

For this reason, supplement safety is considered separately from evidence of benefit.

Important safety considerations include:

• avoiding excessive doses, especially when using multiple products containing the same ingredient;
• checking whether a supplement may interact with chemotherapy, immunotherapy, radiotherapy, surgery, anticoagulants, hormone therapy, or other medications;
• avoiding products that make exaggerated cancer claims;
• choosing reputable brands with transparent labelling;
• using third-party certification directories where possible;
• recognizing that “natural” does not automatically mean safe.

Where possible, patients are encouraged to choose supplements listed in a public third-party certification directory. Certification does not prove that a supplement treats cancer, but it can provide extra reassurance about identity, purity, manufacturing quality, and contamination risk. Independent testing organizations such as NSF describe certification as a way to verify that supplement contents match the label and are tested for quality.

A separate Supplement Buying Guide is included on this site.

Why Some Therapies Are Included Even When Evidence Is Incomplete

Some therapies are included on Cancer Ireland even when the evidence is incomplete.

There are several reasons for this:

• Some therapies are biologically plausible but under-studied.
• Some have early clinical signals but lack large confirmatory trials.
• Some are difficult to study because they involve lifestyle, diet, multi-component protocols, or individualized use.
• Some are low-cost or non-patentable, which may reduce commercial incentives to fund large trials.
• Some are already widely used by patients, making balanced education safer than silence.

The absence of strong clinical evidence does not automatically mean a therapy is ineffective. But it does mean the level of certainty is lower.

On this site, such therapies are included for education, comparison, and critical review — not as proof of effectiveness.

Why Inclusion Does Not Equal Recommendation

Cancer Ireland includes information for patient education and convenience. Inclusion of a therapy, drug, supplement, test, diet, or lifestyle strategy does not mean that it is recommended for every patient, every cancer type, or every stage of disease.

Some interventions may be unsuitable in specific situations. For example, they may interact with treatment, increase bleeding risk, affect liver enzymes, alter immune activity, interfere with surgery, worsen side effects, or be inappropriate for particular cancer types.

The purpose of this site is to help patients understand the evidence, uncertainty, possible mechanisms, and safety issues so they can make better-informed decisions.

Suggested Evidence Labels Used on This Site