Contagious cancer might sound like the plotline to a bad horror movie involving more gore than necessary and a healthy dose of panic, something along the lines of Quarantine. Unfortunately, this time it’s no horror movie - scientists have confirmed the existence of new types of transmissible cancer, or cancer that spreads like a virus. In an article published in Nature, the research team, headed by Stephen Goff, lays out their findings and the implications for further research in the types and transmission of cancer. Though this isn’t the first time scientists have found evidence of contagious cancers, for the first time they’ve found cancer that spreads not only among one species but between multiple similar species. But what exactly does ‘contagious cancer’ mean? How is it spread? And when do we need to be worried?
What Is It?
Currently, experts recognize 8 types of contagious cancer, 5 of which were identified in this study. The other three have been known about for years and don’t affect molluscs; one type of sexually transmitted tumors only affects dogs, and the other two cancers are characterized by facial tumors and are currently endangering the remaining tasmanian devils. While these cancers have no cure, there are treatments that experts hope will lead to an eventual way to halt the wipeout of the tasmanian devils at least.
On the other hand, the cancers currently affecting bivalves (molluscs with “laterally compressed bodies enclosed by a shell consisting of two hinged parts”) are different. Unlike the transmissible cancers in dogs and tasmanian devils, these cancers can spread not only between bivalves of the same species but also between many species (though the species must be similar), such as between clams and cockles, or different species of mussels. The cancer is similar to leukemia and currently, there is no cure.
How Do Scientists Know?
While the existence of these cancers has been known for some time, identifying its ability to move between bivalve species is more recent. Researchers tested cancerous cells for their DNA and then realized that the DNA of the cells didn’t match the host but instead another bivalve. In at least one case, the cells had originated from bivalves of the same species; in another, the cells were from a separate species that appeared to be unaffected (possibly due to a built-up resistance). So how are the cancerous cells being transmitted at all?
One possible method of transmission has to do with the fact that most bivalves are passive filter feeders, and the fact that they live in water. According to the research team that authored the study, it’s possible the dying host of the cancer emits the cancerous cells which can exist for a time in the water without a host. As the cells are suspended in the water, another bivalve might accidentally draw in the cancerous cells and ingest them, thus becoming the new host for the cells. Unfortunately, bivalves generally don’t have high-functioning immune systems and are unable to fight off the cancerous cells, resulting in entire shellfish beds in danger of being wiped out.
Should We Be Worried?
In terms of being affected by transmissible cancerous cells from bivalves, the short answer is ‘no’, though contagious cancer in humans could become an issue eventually. While these particular cancers can spread between different species of bivalves, the species have to be closely related. In addition, the scientists believe the cancerous cells are transmitted because they can exist in the water for a period of time without a host, and it’s unlikely they would survive if airborne. However, the discovery of new types of cancer is incredibly important for scientists studying cancers. By observing the ways in which cancers spread and the changes in the cancerous cells that allow them to spread, scientists can gain better understandings of cancer in humans and identify new approaches for treatments. However, the risk these cancers pose to shellfish beds is significant and probably less rare than originally thought, and scientists will continue to explore the lasting effects of the contagious bivalve cancers.
