Cancer in Dogs: What to Know

A vet answers commonly asked questions about cancer in dogs.

Medically Reviewed by Amy Flowers, DVM on January 21, 2024
6 min read

Carter Swords of Atlanta had been inseparable from her Jack Russell terrier, Possum, for 15 years when he was diagnosed with cancer. “They found a tumor on his bowels and I was devastated,” she says.

Not wanting to put her beloved dog through aggressive treatments, Swords focused on keeping Possum comfortable and enjoying their remaining time together. “The day he died, the sun was shining and the birds were singing, and it just didn’t seem right,” she recalls. “I didn’t know how I would go on without him.”

Unfortunately, like Swords, most dog parents will someday hear that their dog has cancer. It’s the leading cause of death among senior dogs and can show up in younger dogs, too. Heather Wilson-Robles, DVM, a veterinary oncologist and current president of the Veterinary Cancer Society, shares what you should know.

“It’s very common,” Wilson-Robles says. “More than 50% of dogs over the age of 10 will have cancer. There are some cancers that show up pretty frequently in dogs. The most common are melanomas and mast cell tumors – types of skin cancers, lymphomas, and bone cancers. Those are the big ones. We also see anal sac tumors pretty frequently.”

The symptoms are often the same as those in people. “The difference is our dogs can’t tell us what is going on,” Wilson-Robles says. “In many cases, these things are found when you take your dog in for their annual or semiannual checkup.”

“The most common symptom is a lump or bump found during an exam or at home. It could be an enlarged lymph node, limping, or pain,” she says. “We see things like weight loss, fatigue, and decreased appetite. In some older dogs, we hear pet parents say things like, “I just thought she was slowing down because she was getting older.” It turns out they were having symptoms that may have been missed.”

Wilson-Robles recommends spaying or neutering your dog early on. “There’s plenty of good data that suggests the earlier you spay your dog, for example, the less likely she is to get breast cancer,” she says. 

It also helps for your dog to be at a healthy weight. “It doesn’t mean a specific diet – just good-quality food and getting your dog to a healthy body weight through activity and healthy food,” Wilson-Robles says. 

There are also environmental toxins, “some avoidable and some not,” she says. “We do see increased risk in houses where people smoke.”

“Dogs are living longer. We have better vaccines, overall better wellness care, better leash laws, and people are being more responsible. We don’t see as many dogs passing from car accidents as we did years ago. As dogs live longer, they are more at risk of cancer being their cause of death,” Wilson-Robles says. “For average-sized dogs, we see cancers show up in ages 8 to 10, ages 9 to 12 for smaller dogs, and ages 6 to 8 for giant breeds.”

“Absolutely, there is a breed association with cancers. You can tell me a breed, and I can tell you the type of cancer a dog might get,” Wilson-Robles says. “We think about golden retrievers, Bernese mountain dogs, rottweilers, boxers, beagles, Scotties, westies – those breeds are commonly affected by cancer.”

Mixed-breed dogs “may be a little more resilient to cancer, but I do see them in my practice,” Wilson-Robles says. 

“It depends on the cancer,” Wilson-Robles says. “Some cancers are much more likely to be fatal. Things that are localized [in one particular area] are much more likely to be curable. Cancers that have an impact on the whole body have a higher rate of being fatal.”

“There are a lot of cancers with cures – mast cell tumors, soft tissue sarcomas, some of the anal sac tumors. I encourage people to meet with a veterinary oncologist to find out their options.” 

“Cancer is diagnosed in a number of ways,” Wilson-Robles says. “Most often we get a sample with a fine needle aspirate or a biopsy. Imaging can be very helpful, especially in places that are difficult to access such as an MRI for a brain tumor.”

“We are starting to see some blood tests for cancer, such as the Cadet tests for certain blood or bladder cancers,” she notes. “The Nu.Q Veterinary Cancer Screening Test and the OncoK9 tests help us see if cancer is likely, but they do not specify the type of cancer. There are also new companies out there that can help determine the type of lymphoma that is present at the molecular level. These tests are available at most labs.”

“For decades, we used generic and off-label versions of human cancer treatments for dogs,” Wilson-Robles says. “In 2009, the first FDA-approved cancer drug for dogs [became] available. But we still use some of the human cancer drugs, and more are becoming available for dogs.”

“An area that has grown in the last 10 years is matching the treatment with the specific type of cancer,” she says. “We’re also getting a lot better … with a combination of therapies where you have surgical oncologists, radiation oncologists, and medical oncologists working together. That team comes up with an integrated plan to treat your dog’s cancer. When all three arms are working together and everyone is taking care of different needs, the outcomes are a little better.”

“Still, treating cancer doesn’t always make the cancer better. Sometimes it can make things worse. I always recommend working with a veterinary oncologist to help you understand your next steps.”

“This varies based on the type of cancer. There are some cancers that do very well and can be a few hundred dollars to treat. When you get into more complicated cancers that have several specialists, you can easily spend $15,000 or more,” Wilson-Robles says. 

“It also depends on where you live – some areas are more expensive,” she points out. “Many chemotherapy treatments can be several thousands [of dollars], but it’s not your only option. I recommend meeting with a veterinary oncologist [for a few hundred dollars] to talk about a treatment plan” and discuss the standard treatment for your dog’s cancer and any lower-cost options. 

“I recommend having open and frank conversations with your vet medical team – and early on before you’re emotionally bogged down by what is happening. Have a frank discussion about where those lines are for quality of life, and use those as a reference. It’s always going to be hard, but most people really want to do what’s right for their pet,” Wilson-Robles says. 

“I tell people to pick five things your dog really likes doing, and when they’re not doing at least two of those things regularly … let’s have a discussion.”

Another tip: “Get a calendar and put green check marks on good days and red check marks on bad days. We all have bad days, but when your dog is having three or more bad days a week, you should have that conversation.”

“With humans, doctors are trying to [help] patients live 20-30 more years; for children, they’re hoping to help you live 60 more years. The approach is going to be different for a dog,” she points out. “If you have a 12-year-old dog whose average lifespan is 14, we aren’t trying to treat them to live 10-20 more years. Plus, I can’t ask your pet if they want to go through this. I have to work with the pet parent … to determine what is best. For all these reasons, we will work really hard to control the disease and bank on quality of life versus quantity of life. It’s great when we can get both.”