Contagious cancer lineage uncovered in brown bullhead melanoma

Genomic analyses of brown bullhead melanomas from Lake Memphremagog show a single clonal cancer lineage spreading among fish, marking the first confirmed transmissible cancer in a freshwater fish. Tumour mitochondrial and nuclear DNA are more similar across affected fish than to their hosts, with many shared tumour-specific variants and no associated microbes detected, suggesting cancer cells themselves are the infectious agent. The findings raise questions about origin, transmission mechanisms, and potential ecological impacts on brown bullhead populations.