Ecological studyindependent cross-checkabstract checked★ key study I-CAN-117 in-depth review
Random copying errors in cells and cancer
Stem cell divisions, somatic mutations, cancer etiology, and cancer prevention.
Overview
Tomasetti C et al.. Science 2017 · PMID 28336671 · DOI 10.1126/science.aaf9011
About two-thirds of cancer mutations may come from random errors when cells divide; preventable causes still matter.
Does the study support the specific claim? Partly · Methodological quality: moderate
Plain-language summary
Study explained simply
- What did the researchers want to find out?
Estimate sources of cancer mutations.
- How was the study done?
Modelling across countries and genomes.
- How many people, animals or samples were studied?
17 cancer types, 69 countries.
- What was actually found?
Replication errors are a major source.
- How large was the observed effect?
~2/3 of mutations.
- What do the results mean in everyday life?
Not every cancer is caused by lifestyle, but many are preventable.
- What are the study's limitations?
Contested method.
- What does it say about Elawady's specific claim?
Partly supports internal origin, not a 'plan'.
- Do the results apply to Germany and Europe?
High.
- What can explicitly not be concluded from this study?
Purpose or benefit of cancer.
Scientific in-depth review
1. Full reference
- Authors
- Tomasetti C et al.
- Journal
- Science
- Year
- 2017
- Identifier
- PMID 28336671 DOI 10.1126/science.aaf9011
- Verification
- verified – PubMed efetch 2026-10-26 + Crossref
- Retracted
- no
- Corrections
- none
- Extent checked
- abstract only
- Conflicts of interest and funding
NIH grants; COI arrangement managed by JHU (PubMed record)
2. Research question
How much do replication errors in dividing stem cells, environment and heredity contribute to cancer mutations?
3. Study design and population
- Study design
- Ecological study – Ecological and genomic modelling study
- Population
17 cancer types in 69 countries; cancer genome data
- Country
International
- Period
Published 2017
- Sample size
17 cancer types, 69 countries
- Inclusion and exclusion criteria
not stated
4. Methods and endpoints
- Exposure / intervention
Lifetime stem cell divisions
- Comparator
not applicable
- Endpoints
Cancer incidence; mutation origin
- Statistical methods
Correlation; genomic attribution
5. Actual results
- Results
Strong correlation (median 0.80) between cancer incidence and normal stem cell divisions in all countries; replication errors estimated responsible for two-thirds of mutations in human cancers; results stated as consistent with epidemiological estimates of the fraction of cancers preventable by environmental changes.
- Absolute risks
not applicable
- Authors' conclusion
Replication errors play a major role in cancer aetiology; early detection is important for cancers arising from unavoidable mutations.
6. Strengths
- Multinational data
- Two independent approaches
7. Weaknesses
- Mutation share is not the same as share of cases preventable
- Contested methodology
8. Risk of bias
- Orienting tool
- none applicable
- Type of assessment
- simplified assessment (abstract only)
- Full formal assessment
- no
- Overall risk of bias
- some concerns
- Rationale
Ecological correlation; modelling assumptions debated.
9. Assessment of the statistical interpretation
'Two-thirds of mutations' is not 'two-thirds of cancers'; one mutation from smoking can still be necessary for a cancer.
10. Relevance to the specific claim
Supports a kernel of Elawady's view (much cancer arises from internal cellular processes, chance) but explicitly not that external causes are irrelevant.
11. Independent contrary findings
The authors state consistency with epidemiological estimates that a large fraction of cancers is preventable (e.g. I-CAN-02).
12. Transferability to Germany and Europe
High.
13. Overall methodological judgement
Mixed: internal origin of mutations is real; 'not caused by external agents' and 'purposeful plan' are not supported.
| Multidimensional assessment | |
|---|---|
| Authenticity of the source | verified |
| Methodological quality | moderate |
| Risk of bias | some concerns |
| Precision of results | not applicable |
| Directness | indirect |
| Reproducibility | partly replicated |
| Consistency with the overall evidence | mixed |
| Regional transferability | high |
| Adequacy of the interpretation (by the archive) | not applicable |
14. Open questions
15. Linked fact checks
- Cancer is the body's own plan ('a self plan'): body cells are ordered to transform because this was necessary for the person's life; it is not caused by external agents. – Studies with mixed or unclear results
- Chronic disease is mostly a cumulative reaction to what enters the body daily - contaminated food, medicines and cosmetics - not a fate that comes from outside. – Studies contradicting or limiting the claim