Keep It Kosher: Cancer is Contagious Among Clams

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The ocean contains a vast number of living things, including many, many pathogens — from bacteria that thrive on coral to fungi that infect lobsters. A drop of seawater may hold 10 million viruses.

Recently, a team of scientists revealed a frightening member of this menagerie: free-floating cancer cells that cause contagious tumors in shellfish. They found one such cancer in a species of clam. They reported that three more species are plagued with contagious cancers.

The cancers are specific to shellfish and do not appear to pose a danger to humans who eat them. But until now, infectious cancer was considered something of a fluke in the natural world, initially observed only in dogs and Tasmanian devils.

The latest research has made scientists wonder whether infectious tumors are actually more widespread.

“We were always thinking there would be more contagious cancer out there, but we didn’t know where they would be discovered,” said Elizabeth P. Murchison, a cancer biologist at the University of Cambridge who was not involved in the new study.

In the traditional view of cancer, mutations strike a cell. These mutations have several causes, including toxins and viruses.