Introduction:
Clonally transmissible cancers are somatic cell lineages spread between individuals via the transfer of living cancer cells. There are only 3 known naturally occurring transmissible cancers: Canine Transmissible Venereal Tumour (CTVT) in domestic dogs; soft-shell clam disseminated neoplasia; and Devil Facial Tumour Disease (DFTD) in Tasmanian devils. DFTD was first observed in 1996 in north east Tasmania, Australia, and is threatening its host species with extinction. Until now, this disease has been associated with a single aneuploid cancer cell lineage that we refer to as DFT1. Here we describe a second transmissible cancer, DFT2, first located in southern Tasmania in 2014.
Materials and methods:
Histology, cytogenetic profiling and genetic analysis of DFT2 were performed and compared with host tissue and DFT1. Genetic analysis involved polymorphic microsatellite loci, structural variants and MHC loci.
Results:
DFT2 tumors are histologically distinct from DFT1 tumours. 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 it as a second cancer that can be transmitted between devils as an allogeneic, MHC-discordant graft.
Discussion:
These findings indicate that Tasmanian devils have spawned at least two distinct transmissible cancer lineages. The discovery of DFT2 raises the possibility that this species is 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.