Tasmanian devils, Sarcophilus harrisii, are being threatened with extinction by a transmissible cancer called devil facial tumor disease. This gruesome disease has been ravaging the little marsupial carnivores since it was first observed in 1996. And now, researchers have discovered another transmissible cancer that also causes facial tumors in the devils. While these tumors resemble the previously identified ones, they’re genetically distinct, according to new work published in Proceedings of the National Academy of Sciences this week.
With clonally transmissible cancers, living cancer cells are transferred between individuals. We only know of three cancers like this in the wild, and they affect dogs, Tasmanian devils, and soft-shell clams. Devil facial tumor disease (DFTD) is spread by biting, and it causes tumors on the face and inside the mouth. It readily metastasises, killing the animal within months after symptoms appear.
Until now, the disease has been consistently linked to a single cancer cell lineage now designated as DFT1. A team led by University of Cambridge’s Elizabeth Murchison and University of Tasmania’s Gregory Woods discovered a second transmissible cancer, called DFT2, in five devils from southeastern Tasmania in 2014 and 2015. That means the poor Tasmanian devils have given rise to two different transmissible cancers – something that’s rarely observed in any species.
After wild Tasmanian devils with signs of DFTD on the Channel Peninsula were either found dead or trapped, tissue biopsies were collected and tumor samples were drawn through a fine needle (either post mortem or from live devils who were then released). To the naked eye, DFT2 causes facial tumors that appear indistinguishable from those caused by DFT1, but a microscopic examination of the tissues revealed minor though distinguishable differences. DFT1 and DFT2 do not share any detectable similarities at the level of chromosomes, not to mention DFT2 carries a Y chromosome, sharply contrasting with the female origin of DFT1.
In addition to being both histologically and cytogenetically distinct, DFT2 is also genetically distinct from DFT1. While researchers expected DFT2 to be derived from DFT1, "as far as we can tell, DFT2 is a totally new cancer that has arisen independently of DFT1," Woods explains to IFLScience. "The confusion is that both DFT1 and DFT2 appear to be derived from a similar precursor cell, but this has yet to be confirmed." There’s also the slightest possibility that DFT1 fused or transferred some genetic information to a normal cell, creating DFT2.
If Tasmanian devils have spawned at least two distinct transmissible cancer lineages, that means these sorts of cancers may arise more frequently in nature than we think.
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