Outbreaks of leukaemia-like cancer in soft-shell clams may have originated in a single clam.

Mysterious cancers have been affecting clams and other marine bivalves in the United States and Europe since at least the 1970s. Stephen Goff at Columbia University in New York and his colleagues studied the DNA of cancerous and non-cancerous cells from several populations of soft-shell clams (Mya arenaria) along the coast of the eastern United States. The DNA from cancerous cells did not match that of the hosts' other tissues, but the cancer cells were genetically similar to each other, suggesting that they arose from a single ancestor.

Only two other transmissible cancers are known, affecting dogs and Tasmanian devils. However, invertebrates may be particularly vulnerable because they lack a part of the vertebrate immune system that identifies foreign invading cells, the authors say.

Cell 161, 255–263 (2015)