The idea that cancer cells may occasionally acquire DNA from other, normal, cells of the body through a process of horizontal gene transfer, has long been discussed. This would be possible through a variety of mechanisms, including cell fusion, phagocytosis, trafficking of genetic material through tunnelling nanotubules, or other mechanisms. However, an understanding of the frequency and significance of this process in naturally occurring tumours is lacking.
Transmissible cancers, unusual cancers which occur when cancer cells themselves spread between animals as a type of infectious disease, provide a useful system in which to screen for host-to-tumour horizontal gene transfer. Among mammals, transmissible cancers are known only in dogs (a sexually transmitted genital cancer) and Tasmanian devils (two facial cancers spread by biting). In transmissible cancers, host and cancer are genetically unrelated; thus, horizontal gene transfer would be expected to create a strong genetic signal in transmissible cancer genomes.
We designed a genetic screen for horizontal gene transfer in transmissible cancers, and implemented this in dog and Tasmanian devil transmissible cancers. This screen detected evidence of horizontal DNA transfer in transmissible cancers, and raises the possibility that this mode of DNA acquisition is more common in cancer evolution than previously appreciated.