Journal club: Transmissible cancer may not be so rare
Cancer is a disease of our own cells gone wrong. Normally our cells work in harmony with each other, taking cues from each other as to when to proliferate, when to differentiate and when to die. In cancer, mutation takes away this level of regulation, leaving a "selfish cell" that ignores all of these signals and proliferates uncontrollably, even to the point of killing the host.
There have been a handful of rare cases where cancers can actually physically cross-over from one individual to another, such that the second individual is actually growing cancer cells that are not self, but are fully derived from the original host. This has been seen in a few human cases as well as well-described transmissible cancers in Tasmanian Devils and dogs. There was even a recent case study that suggests a tapeworm cancer crossed over into the host. In general, however, it is thought that this type of event is going to be exceptionally rare. Even ignoring the protective effect of our immune system killing foreign cells, it is not like cells from one individual can just float through the air to colonise another. Except, of course, under the water.
A paper just published in Nature looks for transmissible cancers in mussels and clams and finds three examples of cancer cells from one individual clam or mussels infecting and growing in other indiviudals of the same, or even different, species. With high population densities and water flow acting to directly transfer cancer cells, it is probably that transmissible cancers are actually a common feature in many marine environments.
Nature 2016, in press. Widespread transmission of independent cancer lineages within multiple bivalve species. Metzger, Villalba, Carballal, Iglesias, Sherry, Reinisch, Muttray, Baldwin, Goff.
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