Research: Contagious canine cancer

The source of a cancer that affects dogs around the world has been traced by scientists and vets at UCL to a single wolf or dog, which probably lived in China or Siberia more than 250 years ago.

In canine transmissible venereal tumour (CTVT), the cells of the tumour itself are transmitted between dogs during sex. No equivalent form of contagious cancer exists in humans, but the new findings challenge current thinking about the nature of cancer.

Some human cancers such as cervical cancer may be considered to be 'catchable', as they are initiated by viruses transmitted between people.What is unusual about CTVT in dogs, however, is that no virus is involved – the cancer itself is effectively passed on.

In a paper published in the journal 'Cell', veterinarian researcher Dr Claudio Murgia conducted forensic DNA tests on tumour tissues from 16 dogs from around the world affected by CTVT. He found that in all cases, the tumours were genetically different from the affected dog – in other words, the cancer had come from a different dog. A further analysis of 40 tumours archived in vet labs in five continents showed that the tumours were genetically almost identical and demonstrated that CTVT originally came from a single source and has since spread across the globe.

To trace this source, the UCL team - led by Professor Robin Weiss of the UCL Division of Infection and Immunity - worked with geneticists and computer experts in Chicago and compared the DNA in the tumours to that in specific dog breeds.

The results of the study – funded by the Wellcome Trust and the Medical Research Council – show that the cancer most likely first arose in either a wolf or an 'old' Asian dog breed such as the husky or shih-tzu. The number of mutations accumulated in the DNA also enabled the researchers to estimate the age of the disease, which came out at around 1000 years and not less than 250 years old.

Image of long-haired dog courtesy of John Wildgoose (from the Medical Photographic Library).

External links

• UCL Division of Infection and Immunity
• Medical Research Council
• 'Clonal Origin and Evolution of a Transmissible Cancer', by Claudio Murgia, Jonathan K Pritchard, Su Yeon Kim, Ariberto Fassati and Robin A Weiss, is scheduled for publication in the 10 August issue of 'Cell'