Researchers say the dogs are good test subjects since they age much faster than humans. And the dogs behave and respond to treatments much like people do.
That means scientists can get the results of their studies more quickly.
"It's like a compressed biological life span that we can study, the cancer progression and also potentially the response to therapy," said Karin Sorenmo, scientist.
A number of the dogs in the study are now cancer free.
The researchers estimate they are within two years of testing the vaccine on humans.
Without the dogs they would be more than a decade away.