Cancer and infectious diseases frequently appear in the news. This is probably because they scare us, with headlines featuring news of outbreaks of infectious diseases, or suspected causes of cancer. Similarly, there is much interest in developments of better methods of diagnosis, treatment, prevention and eradication.
But imagine if there was a cancer which was infectious. We’re not talking about viruses or bacteria which may lead to the development of tumours (like human papilloma virus in cervical cancer, and helicobacter in stomach cancer). But if the tumour cells themselves were contagious…
Unfortunately there are four known types of transmissible tumour in animals. Transmissible venereal tumour (TVT) in dogs is the feature of this blog post. The others are a tumour of Tasmanian devils (Devil facial tumour disease), a tumour of Syrian hamsters spread by mosquito bites, and a form of leukaemia in soft-shelled clams.
We recently had a case of suspected TVT in a dog. The dog presented with a mass on it’s penis, from which a smear was made and examined (cytology). The mass was removed and slides prepared for microscopic examination (histopathology) which confirmed that it was TVT.
It is thought that the tumour cells originate from a type of cell called a histiocyte. One of the reasons we know these tumours don’t arise from the dog’s own cells is that the tumour cells have fewer chromosomes (less than the 78 normally in a dog), and the chromosomes have a different appearance to dog chromosomes. It has also been shown experimentally that the tumour can be transmitted from one dog to another, and even to other canine species, such as foxes.
The tumour spreads between animals during copulation, licking, biting or other contact with infected animals. The tumour may spontaneously regress, if a sufficient immune response occurs, or the animal can be treated with surgery, chemotherapy and/or radiotherapy.