Dogs can get different kinds of cancers, including one that is transmitted by live cancer cells, which spreads through sexual contact, called canine transmissible venereal tumor (CTVT). Researchers have now traced this cancer back to a single dog, a founder that lived sometime between 4,000 and 8,500 years ago. The findings have been reported in Science.
In this work, scientist Adrien Baez-Ortega of the University of Cambridge and colleagues sequenced tumors from 546 dogs around the world, including two dogs of different breeds from Brazil and Australia that both had CTVT. Their tumor cell genomes had almost two million mutations in common, which aren’t found in normal canine DNA. The scientists found that the CTVT genome has remained very stable over time, and contains variations in its sequence that aren’t in normal canine DNA. This showed that CTVT doesn’t develop in dogs sometimes; it arose one time and has spread ever since, from one dog to another.
The work also suggests that CTVT doesn’t progress much over time. Tumors seem to grow to an optimum state and then stabilize, whichi is unusual because cancerous tumors often pick up new mutations as the cells proliferate. Some of those mutations might not have any impact, while others could be harmful to the tumor. But some mutations can increase growth and resistance to drug treatments.
This work could help researchers learn more about human cancers that grow slowly, and how to limit tumor growth when it doesn’t pose a serious health threat.
"Cancers evolve, and our strategies for managing cancer need to take that into account," commented Carlo Maley, who wrote about this research with Darryl Shibata in Science. In the future, we hope to maintain long-term control over these evolving tumors. CTVT is fascinating because it shows us how cancers might evolve over the long term."
"Most cancers can only evolve for a few decades before they die with their host," Maley added. "CTVT is an incredible natural experiment, which showed us that it doesn't take much for a cancer to reach an optimal state. It is amazing that it did not discover additional adaptations over thousands of years, even as it infected all different breeds of dogs in all different environments around the world."
Learn more about CTVT from the video above.
In other research on unrelated canine cancers, researchers are testing a new vaccine in a trial. Learn more from the video below.