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.

Abstract. A disfiguring and debilitating neoplastic condition known as devil facial tumor disease (DFTD) has been discovered in wild Tasmanian Devils (Sarcophilus harrisii) across 51% of its natural range, with population declines of up to 80% in some areas (C. Hawkins, personal communication). Between 2001 and 2004, 91 cases were examined. The tumors presented as large, solid, soft tissue masses usually with flattened, centrally ulcerated, and exudative surfaces. They were typically multicentric, appearing first in the oral, face, or neck regions. Histologically, the tumors were composed of circumscribed to infiltrative nodular aggregates of round to spindle-shaped cells, often within a pseudocapsule and divided into lobules by delicate fibrous septae. They were locally aggressive and metastasized in 65% of cases. There was minimal cytologic differentiation among the tumor cell population under light and electron microscopic examination. The results indicate DFTD to be an undifferentiated soft tissue neoplasm.

SummaryTransmissible cancers are clonal lineages that spread through populations via contagious cancer cells. Although rare in nature, two facial tumor clones affect Tasmanian devils. Here we perform comparative genetic and functional characterization of these lineages. The two cancers have similar patterns of mutation and show no evidence of exposure to exogenous mutagens or viruses. Genes encoding PDGF receptors have copy number gains and are present on extrachromosomal double minutes. Drug screening indicates causative roles for receptor tyrosine kinases and sensitivity to inhibitors of DNA repair. Y chromosome loss from a male clone infecting a female host suggests immunoediting. These results imply that Tasmanian devils may have inherent susceptibility to transmissible cancers and present a suite of therapeutic compounds for use in conservation.

In the mid 1990s an emerging disease characterised by the development of proliferative lesions around the face of Tasmanian devils (Sarcophilus harrisii) was observed. A multi-disciplinary approach was adopted to define the condition. Histopathological and transmission electron microscopic examination combined with immunohistochemistry help define Devil Facial Tumour Disease (DFTD) as a neoplastic condition of cells of neuroendocrine origin. Cytogenetic analysis of neoplastic tissue revealed it to be markedly different from normal devil tissue and having a consistent karyotype across all tumours examined. Combined with evidence for Major histocompatability (MHC) gene analysis there is significant evidence to confirm the tumour is a transmissible neoplasm.

Immunohistochemical techniques were used to characterize the disfiguring and debilitating fatal neoplastic disease, devil facial tumor disease (DFTD), which has recently affected a significant proportion of the wild population of Tasmanian Devils (Sarcophilus harrisii). The diagnostic values of a number of immunohistochemical stains were employed to further characterize 50 representative cases. The neoplasms were negative for cytokeratin (0/48), epithelial membrane antigen (0/42), von Willebrand factor (vWF) (0/11), smooth muscle actin (SMA) (0/26), desmin (0/47), glial fibrillary acid protein (0/13), CD16 (0/13), CD57 (0/43), CD3 (0/18), and LSP1 (0/16). DFTD cells were positive for vimentin (50/50), S-100 (41/48), melan A (11/39), neuron specific enolase (35/35), chromogranin A (12/12) and synaptophysin (29/30). The cells were negative for amyloid (0/30) and stained negatively with Singh's silver (0/34) but were weakly argyrophilic (3/40) using Grimelius histochemical stain. These staining characteristics are consistent with cells of neuroectodermal origin.