Revealed: Dogs are most at risk of dying from cancer – with medium-sized pups topping the list

A new study shows which dog breeds are most at risk of dying from cancer – and it’s not good news for owners of medium-sized puppies.

By studying mortality data for dogs from three different countries, a biologist in California found that the flat-coated retriever has the highest risk of cancer mortality.

Overall, medium-sized dogs have a higher risk of developing cancer than the very largest or smallest breeds, the study found.

The Scottish Terrier, Bernese Mountain Dog and Bullmastiff are also at ‘significant risk’ of dying from the disease, the expert found.

Meanwhile, breeds with the lowest risk of cancer include Pomeranian, Miniature Pinscher, Shih Tzu and Chihuahua.

The study was conducted by Leonard Nunney, a professor of biology at UC Riverside in California, and published in the Royal Society Open Science.

“Cancer is one of the leading causes of death in domestic dogs, but deaths from cancer vary widely by breed,” he says in his article.

‘Some of these breed differences in cancer risk may be due to the effects of inbreeding.’

Professor Nunney analyzed dog mortality rates based on three different data sets – one each from the US, Britain and Finland.

For the results, he looked at dog breeds that appear in at least two of the three data sets – 85 breeds in total.

He found that the smallest dogs, including Pomeranians, Miniature Pinschers, Shih Tzus and Chihuahuas, have about a 10 percent chance of dying from cancer.

Dalmatians and Bulldogs were among those at slightly higher risk – about 20 percent.

By comparison, many relatively large breeds, such as the Burmese Mountain Dog and Bullmastiff, have a 40 to 50 percent chance of dying from cancer.

But the Flat-Coated Retriever – a hunting dog breed native to England – had the highest cancer mortality rate, at about 60 percent.

The expert discovered that the breed develops a type of sarcoma at a higher frequency than it should have for its size.

Despite the general trend for small breeds to be at lower risk, the Scottish Terrier is a small breed with an unusually high risk of death from cancer compared to other small breeds.

‘Terriers generally get more cancer than expected for their size,’ Professor Nunney said.

Just like humans, dogs develop cancer due to genetic factors and environmental stressors.

It’s common for cells to acquire errors or mutations as they divide and form copies of themselves – the process that can lead to cancer.

Larger animals, and those that live longer, have more cells and a longer lifespan during which these cells divide – so they should have more opportunities to acquire mutations that eventually become cancer.

‘Research in humans shows that tall people get more cancer than short people,’ says Professor Nunney.

‘It involves an increase of about 10 percent over the baseline risk for every 10 centimeters of height.’

However, the very largest breeds, such as Great Danes, have less cancer than medium-sized breeds, the results show.

This is due to a yet unexplained phenomenon: the life expectancy of dogs decreases as body size increases.

‘For every kilo increase in typical breed size you lose about two weeks of life,’ Professor Nunney added.

‘A very large dog, you’re lucky if it lives longer than nine years, while small dogs can live up to fourteen years.’

Cancer is primarily a disease of old age, so due to a shorter lifespan, the largest dogs have a lower risk of cancer than medium-sized dogs.

In other words, larger dogs may not die from cancer as often as medium-sized dogs, but they are likely to have a shorter lifespan anyway.

Professor Nunney warns that some breeds may have had an increased risk of cancer due to inbreeding – the mating of closely related dogs together, usually of the same breed.

Mixed-breed dogs live about 1.2 years longer than purebred dogs of similar size, a previous study found. This indicates that a decrease in inbreeding levels leads to a longer lifespan of dogs.

“Inbreeding (and the associated loss of genetic diversity) is a known cause of increased incidence of hereditary diseases,” the expert adds.

Like the symptoms in humans, the warning signs of cancer in dogs include lumps and bumps, abnormal discharge, non-healing wounds, weight loss, change in appetite, and coughing or difficulty breathing.

According to the NC State University Veterinary Hospital, up to 80 percent of skin lumps in pets are not cancerous.

“But consulting with your vet is the only way to be sure,” it says.