Brown bullhead catfish melanoma represents a novel transmissible cancer - Nature

What the report says

Nature reported that researchers have identified melanomas in brown bullhead catfish from Lake Memphremagog, which straddles Vermont and Quebec, as a likely new naturally occurring transmissible cancer. The finding is based on whole-genome sequencing of tumors and matched non-tumor tissue from affected fish, along with comparisons to unaffected fish. The study says tumor genomes were more similar to one another than to the fish carrying them, a key signal that the cancer cells share a common origin and have spread between animals.

The outbreak has been observed since 2012, when anglers and biologists noticed many brown bullheads with raised black lesions. A previous study cited by Nature found malignant melanomas in 23% to 37% of sampled brown bullheads between 2014 and 2017, a much higher rate than generally reported elsewhere. Because the lake supplies drinking water to more than 175,000 people, the unusual cancer burden had raised concern about possible contaminants or infectious causes.

According to the paper, the tumors carried hundreds of thousands of genetic variants shared across samples but absent from the hosts’ normal tissue, a pattern the researchers say is far beyond what would be expected in ordinary cancers arising independently in each fish. Microbiome analyses described in the article had not identified a virus or other microorganism unique to diseased fish, leaving the cancer cells themselves as the suspected transmitting agent.

If confirmed, the brown bullhead disease would become the fourth documented type of naturally occurring transmissible cancer in animals, after examples in dogs, Tasmanian devils and several bivalve species. The work leaves open major questions about how the cancer began, how it moves between fish and what it may mean for local populations.