The researchers add that this occurrence of species-hopping cancer in an already small set of animals needs more study, and they intend to find out how they spread.
Although cancer can spread to distant parts of a body, in an often-deadly process known as metastasis, it generally stays within the individual in which it originated.
These invading cells "seem to be the most frequent causes of these leukemia-like cancers in mollusks", said study senior author Stephen Goff, a molecular biologist at Columbia University Medical Center in NY. The cancerous hemocytes had different genotypes from that of the solid tissue found in the animals with cancer, indicating that the cancer cells had originated in another mussel, the researchers reported.
In each species, the researchers discovered that the cancers were caused by independent clones of cancer cells that were genetically distinct from their hosts. In this species, however, the neoplasm genotype matched that of Venerupis corrugata, a different but related species that lives in close proximity to the golden carpet soft shell clams but does not have evidence of leukemia.
The new study, led by a team at Columbia University in NY, reveals more species of shellfish are vulnerable to transmissible forms of cancer, suggesting it may be far more widespread than previously thought. Tumour cells might be released when an animal dies, but Goff notes that the molluscs' faeces are also full of blood cells.
We typically don't think of cancer as a disease we can catch from another person, but that isn't necessarily the case for animals living on the seafloor.
Murchison says that the spreading of cancer between individuals requires the tumour to elude an immune attack, and she expects that the barrier is even higher between species. Tasmanian devils spread cancers by biting each other on the face, and dogs transmit the diseases through sexual intercourse, but neither method is a possibility with these immobile shellfish.
It is still unknown how the cancer cells are able to jump between individuals, Goff said: "It may just be that they're pooping these cells into the ocean". The scientists determined that this cancer was as a result of cross-species transmission. The cells somehow transfer cancer from one species to another. Maybe human beings may even come to know more about the role of cancer in their own species via a thorough analysis of this transferable cancer found in marine species.
"Now that we have observed the spread of cancer among several marine species, our future research will investigate the mutations that are responsible for these cancer cell transmissions", Goff said in the news release.
The scientists detailed their findings online June 22 in the journal Nature.