Do Cancers Not Lose to Evolution? ― The Discovery That Rapidly Evolved Animals Have "Fewer Malignant Tumors"

Do Cancers Not Lose to Evolution? ― The Discovery That Rapidly Evolved Animals Have "Fewer Malignant Tumors"

2025年11月13日 00:42

"Rapidly Changed Bodies" Were Also Strong Against Cancer?

"Larger animals are not necessarily more prone to cancer"—a long-standing notion (Peto's paradox) has been challenged by comparative oncology, and now another new piece has been added.It suggests that animals whose body sizes evolved rapidly have a lower frequency of malignant tumors. The study was conducted by a team from University College London (UCL), University of Reading, and Johns Hopkins University, and was published in **PNAS (Proceedings of the National Academy of Sciences)** on November 6, 2025. A general audience article was also released on Phys.org on November 11.oro.open.ac.uk


Key Points of the Study: "Dynamics of Evolution" Differed Between Benign and Malignant

The analysis modeled autopsy-based tumor data from 77 bird species and 87 mammal species, linking it with body size (weight), the rate of body size evolution, and the **rate of phylogenetic diversification (speed of speciation)**. The results are clear.

  • Malignant Tumors: Lineages with faster body size evolution have lower prevalence (common in both birds and mammals).

  • Benign Tumors: No similar decrease was observed.

  • Birds: Lineages with higher diversification rates tend to have increases in both benign and malignant tumors. In mammals, no significant relationship was observed, showing different patterns between groups.The authors interpret that during the rapid change of body size, cancer-specific defense mechanisms (such as mechanisms to suppress metastasis or invasion) could be selected, while benign tumors, which may appear as mild disturbances in cell proliferation, are less likely to be strongly selected against. The "diversification = tumor increase" trend in birds is explained by the hypothesis that bird genomes are small and compact, making them more susceptible to instability associated with speciation, such as chromosomal rearrangements.phys.org


How Was It Verified?

Statistically, Bayesian multivariate phylogenetic GLMM was used to control for non-independence due to common ancestry among lineages. Differences in observational efforts, such as the number of autopsies, were also incorporated into the model. While it does not assert causation, when considering "how large the body is" along with "how quickly it became larger (or smaller)," signs emerge that only malignant tumors are strongly influenced by selective pressure.The speed of evolution is highlighted as a key factor.oro.open.ac.uk


Background: "Re-examination of Conventional Wisdom" in 2025

The same authors published another report in February 2025, prompting a re-evaluation of the conventional "larger animals have more tumors" paradox. This current report extends that line of inquiry by focusing on **not just "size" but "how size changes,"** distinguishing between malignant and benign, which is a novel approach.University College London


A "Bridge" from Evolutionary Biology to Cancer Research

The perspective that "cancer can be viewed not only as a cellular runaway but also in the context of evolution" contributes to understanding treatment resistance. The "cancer-specific" defenses enhanced in rapidly evolving lineages align well with the concept of targeting the evolutionary properties of tumors, such as metastasis, dormancy, and environmental adaptation. Indeed, the authors interpret the result of "only malignancy decreases" as evidence of process-specific defenses like metastasis suppression. While there is a leap to directly apply this to human medicine, the axis of evolutionary speed provides clues to explore why some animals are resistant to cancer.oro.open.ac.uk


Why Did Differences Emerge Between Birds and Mammals?

The "diversification = tumor increase" trend was observed in birds but not in mammals. Birds have small, dense genomes, and changes associated with speciation, such as chromosomal rearrangements and gene fusions, tend to work in a tumor-promoting manner—this is the authors' hypothesis. The phenomenon where gene fusions, such as those seen in human prostate cancer (e.g., TMPRSS2–ERG), shuffle information and increase malignancy is well-known in cancer biology. The crosstalk between evolution and genome structure may be the key to differences between groups.phys.org


Points to Note: Limitations and Next Steps

  • Bias in Data Sources: Much of the data relies on autopsy records, with differences in captive environments, observational efforts, and diagnostic granularity.

  • Distinction Between Benign and Malignant: It may be affected by pathological consistency and oversight.

  • Correlation and Causation: The speed of evolution is a correlation indicator, and direct mechanisms (such as immunity, DNA repair, redundancy of tumor suppressor genes) require future molecular-level verification. Nonetheless, the pattern of "only malignancy inversely correlates with the speed of evolution" is reported as a reproducible strong signal and is included in the November 11 issue of the PNAS table of contents.oro.open.ac.uk


SNS Reaction Digest (Summary)

As of the current moment (November 12, 2025), this topic is spreading through university public relations (EurekAlert!, University of Reading) and science media (Phys.org, Bioengineer.org). The following points are being shared within the research community:

  • "The design that separated benign and malignant is good"—a step forward in comparative oncology that does not lump together two diagnostically different categories.

  • "Examination of biases in autopsy data and statistical assumptions is necessary"—particularly in estimating speciation rates and pathological consistency.

  • "Application to human medicine should be cautious"—however, it is a plus for ideas in research on treatment resistance and metastasis. (Note: For primary sources of dissemination and official information, see below)
    EurekAlert!


Mapping the Research: The Current State of Comparative Oncology

This study aligns with the reevaluation presented by the same team in early 2025, which questioned the notion that **"larger species have more cancer", and further delves into "how quickly they became larger".The trend of exploring genetic resistance to cancer in elephants and whales (such as increased p53 copy number and duplication of tumor suppressor genes) is also in line.By integrating multiple axes such as species size, lifespan, genome structure, and evolutionary speed, a map is being drawn to tackle **"cancer as an evolutionary phenomenon."PMC


Related Articles

Study Finds Fewer Cancerous Tumors in Rapidly Evolving Animals
Source: https://phys.org/news/2025-11-cancerous-tumors-common-rapidly-evolving.html

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