Male dogs are up to five times more likely than females to develop a contagious type of cancer, scientists have said.
Canine Transmissible Venereal Tumour (CTVT) is an extremely unusual type of cancer. While almost every other cancer cannot survive the death of its host, CTVT’s living cells physically transfer from one dog to another in a process thought to have been taking place for as long as 11,000 years.
Parasite-like cancer, which responds well to chemotherapy and is rarely fatal, commonly grows in dogs’ genitals and is usually transmitted during mating. But in rarer cases, it can spread to the mouth and nose when dogs sniff or lick other dogs in these areas.
Scientists from the University of Cambridge have now found evidence suggesting that male dogs are significantly more likely to develop this rarer type of CTVT than females – likely because they spend more time taking part in the activities which spread the cancer.
In a study published on Sunday in the journal Veterinary Record, researchers reviewed a database of nearly 2,000 cases of CTVT from around the globe and found that only 32 tumours affected the nose or mouth. Of these, 27 cases were in male dogs.
Dr Andrea Strakova, from the University of Cambridge’s Department of Veterinary Medicine, performed this study with colleagues from the Transmissible Cancer Group, led by Professor Elizabeth Murchison.
“We think this is because male dogs may have a preference for sniffing or licking the female genitalia, compared to vice versa,” said the study’s first author Dr Andrea Strakova, first author of the study.
“The female genital tumours may also be more accessible for sniffing and licking, compared to the male genital tumours.”
CTVT is one of only eight known types of transmissible tumours, with two found in Tazmanian Devils and five in shellfish such as mussels and clams. It first arose millennia ago, from the cells of one individual dog, and is regarded as the oldest and most prolific cancer lineages in nature, having spread to dog populations worldwide.
While uncommon in the UK, case numbers have risen in the past decade, in a development likely linked to the import of dogs from abroad.
“Although canine transmissible cancer can be diagnosed and treated fairly easily, veterinarians in the UK may not be familiar with the signs of the disease because it is very rare here,” said Dr Strakova, adding: “We think it’s important to consider CTVT as a possible diagnosis for oro-nasal tumours in dogs.
“Treatment is very effective, using single agent Vincristine chemotherapy, and the vast majority of dogs recover.”
The most common symptoms of the oro-nasal form of the cancer are sneezing, snoring, difficulty breathing, nasal deformation or bloody and other discharge from the nose or mouth.