# Scientists Identify Fourth Case of Transmissible Cancer in Animals Researchers discover contagious melanoma spreading among brown bullhead catfish in Lake Memphremagog. - **Source:** [Science News | Latest Updates on Scientific Discoveries | The Hindu](https://www.thehindu.com/sci-tech/science/) - **Published:** 2026-10-20 - **Topic:** [Business](https://brifing.si/c/business) - **Original article:** - **On Brifing:** https://brifing.si/s/1d8df3a5-c480-457b-96f6-9296e7150647 ## Discovery of Transmissible Melanoma Researchers from the University of Vermont identified a fourth instance of naturally occurring contagious cancer in animals. The study focuses on brown bullhead catfish residing in Lake Memphremagog, located between Quebec and Vermont. Since 2013, approximately 30% of the catfish population in this specific lake has been afflicted with aggressive melanoma skin cancers. ## Genomic Evidence of Transmission Scientists compared the genomes of melanoma cells with normal cells from affected fish to determine the origin. They discovered that the cancer cells originated from a distantly related fish rather than the host itself. Mitochondrial DNA analysis revealed significant mutations, confirming that these tumor cells act as an infectious entity moving between hosts. ## Excluding Conventional Pathogens The research team conducted extensive screenings of tumor and normal tissues to identify potential viruses or microbial agents. No unique pathogens were found in the affected fish, leading researchers to conclude that the cancer cells themselves are the infectious agents. This genomic evidence supports the classification of this disease as a transmissible cancer. ## Mechanisms of Aquatic Spread Transmission likely occurs through physical interactions during spawning in small areas of the lake. Researchers speculate that cancer cells may also spread indirectly through the aquatic environment. These cells could potentially graft onto a new host through the gills, skin, or mouth, similar to the passive transmission observed in various bivalve mollusc species. ## Comparison to Known Cases Previous instances of transmissible cancer include venereal tumors in dogs, which spread through sexual contact, and oral-facial cancer in Tasmanian devils, transmitted via biting. Unlike these, bivalve molluscs experience passive transmission through seawater. The catfish case provides a new model for understanding how cancer cells can successfully exploit entirely different organisms as hosts. ## Immune System Evasion Clues This research offers potential insights into organ transplant rejection in humans. The affected catfish do not reject the foreign cancer cells, despite them being clearly non-self. Studying how these tumors evade the host's immune surveillance could reveal critical biological mechanisms that prevent the body from attacking transplanted organs or foreign tissues. ## Cancer as Cooperation Breakdown The study reinforces the theory that cancer is not merely a product of specific mutations but a fundamental breakdown of multicellular cooperation. When cells refuse to cooperate and proliferate at the expense of others, they disrupt the organism. Transmissible cancers represent an extreme case where cells break rules across different individual organisms. ## Significance of the Findings While the existence of transmissible cancer is no longer a surprise to the scientific community, this fourth instance expands the understanding of the disease. By documenting how these cells survive and spread in a natural environment, researchers gain a deeper perspective on the evolutionary potential of cancer cells to act as independent parasites. ## Sources covering this story - https://www.thehindu.com/sci-tech/science/scientists-unearth-new-instance-of-contagious-cancer-in-animals/article71604404.ece — --- _Summary written by Brifing from the original reporting. Copyright in the original article belongs to its publisher; read the full piece at the link above._