Is cancer contagious?

In some living beings in the ocean, there are indications that cancer could be contagious (meaning, it could spread from one person or organism to another, typically by direct contact).

The ocean contains a vast number of living beings, including many bacteria to fungi that infect lobsters.

Recently, a team of scientists revealed a scary finding: free-floating cancer cells that cause contagious tumours in shellfish. Last year they found one such cancer in a species of clam.

On 29 June 2016, three more species plagued with contagious cancers were reported.

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 tumours 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.

A decade ago, scientists discovered two exceptions. In the 1990s, Tasmanian devils in Australia began developing deadly face tumours. But DNA in the tumour cells did not match that of the affected animals, studies showed.

For years, Tasmanian devils and dogs were the only species known to contract contagious cancer.

But last year Stephen P Goff, a molecular biologist at Columbia University, and his colleagues found contagious cancer in softshell clams.

Carol Reinisch, a marine biologist at Environment Canada, found that the cancer clustered in populations, as if it were caused by an outbreak of some sort. She suspected a cancer-causing virus moving from host to host.

With eight contagious cancers now on the records, Murchison has started to wonder if they are not as peculiar as previously thought. ‘They might be emerging fairly often,’ she said.

So should people worry about an outbreak of infectious cancer? ‘I don’t think we should be starting to panic,’ Murchison said.

There have been rare reports of people transmitting cancer. Yet it’s not inconceivable that a human cancer might gain that power.

The new research ‘does raise the possibility that these types of diseases could arise in humans,’ said Carol Reinisch.