A leukaemia-like disease known as disseminated neoplasia can be transmitted within multiple species of bivalve - including mussels and carpet shell clams - and may also spread from one bivalve species to another. The results, which are published online in Nature this week, suggest that transmissible cancers are widespread among marine bivalves.
Although most cancer cells remain within the individual in which they arise, isolated instances of transmission of cancer cells from one individual organism to another has been previously documented in Tasmanian devils, dogs and soft-shell clams.
Stephen Goff and colleagues collected mussels (Mytilus trossulus), cockles (Cerastoderma edule) and golden carpet shell clams (Polititapes aureus) from various localities in Canada and Spain and screened them for neoplasia. Through genetic analysis of cancer and host tissues, they show that cancer cells in some of the bivalves were not derived from the host, but probably arose from a single clonal origin. Specifically, the authors find that neoplasias in all three species are attributable to transmissible cancer lineages. However, genetic material extracted from cancer cells in golden carpet shell clams showed no genetic match with this species, indicating instead that the cancer cells originated in a different species, the pullet shell clam (Venerupis corrugata).
These findings suggest that the transmission of cancers between individuals within a species may be more common than previously thought and that it can even cross the species boundary, note the authors. These transmissible cancers show the remarkable ability of tumours to adapt, survive and propagate, they add.
“Although the mechanisms of cancer transmission remain unclear, the immobile nature of these filter-feeding invertebrates suggests that cancer cells may float through the marine environment and enter their hosts by breaching the digestive or respiratory tracts,” comments Elizabeth Murchison in an accompanying News & Views article.