The clonal nature of DFTD was first suggested based on cytogenetic evidence indicating that DFTD tumors carry a distinctive aneuploid karyotype ( 9). Results Gross and Histological Characteristics of DFT2. The discovery of DFT2 changes our perception of transmissible cancers as exceptionally rare and bizarre natural occurrences, and challenges our understanding of the processes that cause somatic cells to depart from their hosts and become transmissible cancer lineages. These findings suggest that Tasmanian devils may be particularly prone to this type of disease, or alternatively, that transmissible cancers are generally more common than previously detected. Given the rarity of known transmissible cancer clones, it is remarkable that a second clone has emerged in Tasmanian devils. This finding indicates that DFTD tumors can be caused by at least two distinct transmissible cancer clones. However, DFT2 bears no detectable genetic or cytogenetic similarity to DFT1 and the tumors that it causes are histologically distinct. This second cancer, DFT2, manifests as facial tumors that are grossly indistinguishable from those caused by the original DFTD clone, now designated DFT1. Here we report the discovery of a second transmissible cancer in Tasmanian devils. More generally, our findings highlight the potential for cancer cells to depart from their hosts and become dangerous transmissible pathogens. 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. 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. 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. DFT2 bears no detectable cytogenetic similarity to DFT1 and carries a Y chromosome, which contrasts with the female origin of DFT1.

DFT2 causes facial tumors that are grossly indistinguishable but histologically distinct from those caused by DFT1. Here we describe a second transmissible cancer, DFT2, in five devils located in southern Tasmania in 20. Until now, this disease has been consistently associated with a single aneuploid cancer cell lineage that we refer to as DFT1. The Tasmanian devil transmissible facial cancer was first observed in 1996, and is threatening its host species with extinction. There are only three known naturally occurring transmissible cancers, and these affect dogs, soft-shell clams, and Tasmanian devils, respectively. Clonally transmissible cancers are somatic cell lineages that are spread between individuals via the transfer of living cancer cells.

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