A second transmissible cancer in Tasmanian devils.

Clonally transmissible cancers are somatic cell lineages that are spread between individuals via the transfer of living cancer cells. There are only three known naturally occurring transmissible cancers, and these affect dogs, soft-shell clams, and Tasmanian devils, respectively. The Tasmanian devil transmissible facial cancer was first observed in 1996, and is threatening its host species with extinction. Until now, this disease has been consistently associated with a single aneuploid cancer cell lineage that we refer to as DFT1. Here we describe a second transmissible cancer, DFT2, in five devils located in southern Tasmania in 2014 and 2015. DFT2 causes facial tumors that are grossly indistinguishable but histologically distinct from those caused by DFT1. DFT2 bears no detectable cytogenetic similarity to DFT1 and carries a Y chromosome, which contrasts with the female origin of DFT1. DFT2 shows different alleles to both its hosts and DFT1 at microsatellite, structural variant, and major histocompatibility complex (MHC) loci, confirming that it is a second cancer that can be transmitted between devils as an allogeneic, MHC-discordant graft. These findings indicate that Tasmanian devils have spawned at least two distinct transmissible cancer lineages and suggest that transmissible cancers may arise more frequently in nature than previously considered. The discovery of DFT2 presents important challenges for the conservation of Tasmanian devils and raises the possibility that this species is particularly prone to the emergence of transmissible cancers. More generally, our findings highlight the potential for cancer cells to depart from their hosts and become dangerous transmissible pathogens.

We thank Bill Brown, Phil Iles, Billie Lazenby, Jacinta Marr, Jane McGee, Sarah Peck, Holly Wiersma and Phil Wise for assistance with sample collection and curation. Adrian Baez-Ortega, Andrew Davis, Jo Hanuszewicz, Gina Kalodimos, Amanda Patchett, Narelle Phillips, Elizabeth Reid Swainscoat, Jim Richley, Rachel Stivicic and Jim Taylor assisted with surveying, laboratory analysis, data processing and display. We are grateful for support received from Mike Stratton, the Wellcome Trust Sanger Institute (WTSI) sequencing and informatics teams and the WTSI Cancer Genome Project. This work was supported by a Wellcome Trust Investigator Award (102942/Z/13/Z) and by grants from the Australian Research Council (ARC-DP130100715; ARC-LP130100218). Support was provided by Dr Eric Guiler Tasmanian Devil Research Grants and by the Save the Tasmanian Devil Program. JMCT was partly supported by a Marie Curie Fellowship (FP7-PEOPLE- 2012-IEF, 328364). Sequences associated with this paper have been deposited in Genbank with accession numbers KT188437 and KT188438.