in 2015, a second genetically distinct strain of dftd was identified, which was tetraploid, not diploid like the main form of the cancer. the tetraploid form has been linked to lower mortality rates. the cell type origin of this strain of dftd is unknown. increased levels of tetraploidy have been shown to exist in the oldest strain of dftd as of 2014, which correlates with the point at which devils became involved in a dftd removal programme. because ploidy slows the tumour growth rate, the dftd removal programme has been suggested as a selective pressure favouring slower-growing tumours, and more generally that disease eradication programmes aimed at dftd may encourage the evolution of dftd. the existence of multiple strains may complicate attempts to develop a vaccine, and there are reports of concerns that the evolution of the cancer may allow it to spread to related species such as the quoll.