Telomere-driven karyotypic and molecular convergence mimics the transmissibility of cancer in the Tasmanian devil

The current mainstream theory of a transmissible cancer cell lineage in Tasmanian devils was originally based on the discovery of similarly rearranged chromosomes in facial cancers of unrelated individuals (devil facial tumor type 1, DFT1) (Pearse and Swift 2006). Several karyotypic variants of this unique transmissible cancer strain have been described in the literature since the original report (Pearse et al. 2012), mostly based on the analysis of Giemsa (G)-banded chromosomes. Nevertheless, recent evidence published by Pye and colleagues of a karyotypically distinct cancer cell line (DFT2) in a devil population in southeast Tasmania (Pye et al. 2016) make the scenario of a transmissible cancer lineage very unlikely. According to this study, the facial cancers of five male individuals bore no detectable cytogenetic similarities to DFT1, yet in all five tumors similarly rearranged chromosomes were present. Furthermore, DFT2 cells harbored a Y chromosome, which has been reportedly missing in DFT1 samples. Among all the DFT2 cases, no evidence for shared DNA markers with DFT1 could be found, and the authors concluded that based on microsatellite analysis DFT2 tumors were no more similar to DFT1 than they were to their hosts, or to other devils in the population (Pye et al. 2016).