Contagious cancer cells are ‘widespread phenomenon’ in sea, scientists say. The discovery of infectious cancers – once thought to be rare in nature – in three different kinds of shellfish ‘raises questions about the implications for cancer transmission in humans’, expert says.
Direct transmission of cancer among some marine animals may be more common than once thought, suggests a new study published in Nature by researchers at Columbia University Medical Center (CUMC).
CONTAGIOUS CANCER FOUND IN CLAMS AND MUSSELS: HOW DID THAT HAPPEN?
The study, led by Stephen Goff, PhD, the Higgins Professor of Biochemistry in the Department of Biochemistry & Molecular Biophysics and the Department of Microbiology & Immunology at CUMC in collaboration with researchers from Canada and Spain, revealed that in several species of bivalves, including mussels, cockles, and clams, can have contagious cancer cells that spread from animal to animal through the sea water. The contagious cancer, known as disseminated neoplasia, is a leukemia-like disease that affects bivalves in many parts of the world.
Researchers found mussels, cockles and clams, collected off the coasts of Canada and Spain, that had been infected with tumors which originated in another individual. Contagious cancer cells are spreading between different animals and even different species in the sea, according to new research which raises the prospect of the disease becoming infectious in humans. Some of Which Are:
- Mussels (Mytilus trossulus) at Copper Beach in West Vancouver, Canada
- Cockles (Cerastoderma edule) collected in the ria of Arousa in Galicia, Spain
- Golden carpet shell clams (Polititapes aureus) collected in the ria of Arousa in Galicia, Spain.
In the northwest coast of Spain, a delicious clam called the golden carpet shell is suffering from an extraordinary type of cancer—a contagious leukemia.
Almost every other case of cancer in animals—including humans—begins when a single cell in an individual starts growing and dividing uncontrollably, producing a tumor. If the tumor kills its host, it dies too. But the clam’s leukemia is caused by cancer cells that have become independent parasites; they can travel between individuals, creating fresh tumors in each new host.
And if that didn’t astonish enough, this transmissible tumor didn’t even originate in a golden carpet shell. Instead, its genes reveal that it first arose in a related species—the pullet shell. It’s the first known cancer that not only jumps into new hosts but has, at least once, leapt over the species barrier.
Some cancers are caused by contagious things like HPV, the virus that causes cervical cancer, or Helicobacter pylori, a bacterium that causes stomach cancer. But in these cases, the tumor cells themselves stay put. It’s so exceptional for cancers to become infectious in their own right that until a year ago, scientists knew of only two types that did so. One is a facial tumor that infects Tasmanian devils. It evolved recently, spreads through bites, and threatens the future of its hosts. The second is a far older veneral tumor that affects dogs. It arose 11,000 years ago and has spread to six continents.
A third example emerged last year. Along North America’s east coast, soft-shell clams were dying from a strange type of leukemia. Michael Metzger and Stephen Goff, scientists from Columbia University, studied these cancers and found that they were all genetically identical to each other, but genetically distinct from their hosts. That’s the same pattern seen in the Tasmanian devil and dog tumors—a clear sign that these cancers arrive in their hosts, rather than originating from them. They drift through the sea, these selfish shellfish cells, traveling from one cancer-ridden clam to another.
Intrigued, Metzger and Goff polled their marine biologist colleagues and learned that many other shellfish species are afflicted by similar rapidly spreading leukemia’s. They collected cockles and golden carpet shell clams from the coast of Spain, and mussels from the coast of Vancouver. In all three cases, they found the same signature pattern: a genetic match between all the tumors, and a mismatch between each tumor and its respective host.
Writing in a paper published this week in the journal Nature, the authors explain: ‘Our findings show that transmission of cancers between individuals within a species may be more common than previously assumed, and that transmission can even occur between species.’
But the team also references the rare case of an HIV positive man in Colombia who is believed to have contracted cancer from a tapeworm living inside his gut.
At the end of 2015, a medical journal reported a case study of the 41-year-old who died from cancerous tumors in his lungs, which are believed to have been passed to him by the parasite.
The authors write: ‘The recent report…highlights the possibility that transmissible tumors could arise in humans.’
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