Catfish skin cancer spreads between individuals, a rare natural transmissible cancer in nature

Summary

From Nature News: A Vermont study reports a skin cancer in brown bullhead catfish that can pass between individuals, making it one of only a few naturally transmissible cancers observed in nature.

• Transmissible cancers involve cancer cells moving between hosts rather than pathogens
• Other known cases include Tasmanian devils, dogs, and shellfish, illustrating cross-species cancer spread
• The catfish transmission route remains under investigation, with hypotheses including mating behaviour or waterborne transfer
• Humans show no evidence of a naturally spreading cancer; studying these systems provides insight into cancer evolution and immune evasion

Author: Nature

Overview of the discovery

Scientists in Vermont have identified a skin cancer in brown bullhead catfish that can spread from one fish to another. The researchers describe it as the fourth naturally transmissible cancer found in nature, with cancer cells themselves propagating in a new host without any virus or parasite involved. This finding places catfish alongside better known examples such as Tasmanian devils facial tumour disease, canine transmissible venereal tumour, and a transmissible cancer in shellfish, underscoring that cancer can move across individual organisms, not just within a single host species.

Transmission across species

The article outlines how transmissible cancers spread in other animals: Tasmanian devils through direct contact during mating and fighting, dogs via damage to genital membranes during mating, and shellfish through cancer cells released into water that other individuals filter and ingest. For catfish the precise route remains under study, with researchers suggesting it could involve mating behaviours or environmental uptake of cancer cells from water, drawing parallels to the shellfish transmission pathway.

Why these cancers are rare

Transmissible cancers require living cancer cells to migrate to a new host and establish in a different immune system. A healthy immune system recognises foreign cells and attacks them, a barrier that often prevents cross-host disease. Genetic diversity within species further complicates cross-host survival, with Tasmanian devils being a notable exception due to their unusually low genetic diversity which facilitates tumour spread. The fragility of cells means that, even after escape, cancer cells often die before establishing in a new host, which is why direct host-to-host routes are common in known transmissible cancers.

Implications for human cancer research

Although there is currently no evidence of a naturally spreading cancer in humans, studying transmissible cancers in other animals can illuminate fundamental questions about cancer evolution, immune evasion, and cross-species transmission. These natural experiments provide a window into tumour biology that complement what is learned from human cancers alone.

Closing takeaways

The Vermont catfish discovery expands our understanding of cancer dynamics in nature and highlights the importance of comparative oncology for revealing how cancer cells adapt and spread in diverse hosts. While it does not imply a human health risk, it emphasizes the broader relevance of studying transmissible cancers to grasp the immune system's role in cancer control.