Pet Chemotherapy: Frequently-asked Questions

Medical articles
sick husky getting examined at the vet

Whether you’ve faced pet chemotherapy decisions or not, we hope you find answers to these FAQs useful.

Why don’t pets go bald from chemotherapy?

Some pets do go bald, actually. Most don’t, however, because their coat is not continually growing.

“A dog’s hair grows in two stages – anagen, which is where it grows, then telogen, which is where it reached the point it should grow to, then stops growing,” says Jennifer Locke, DVM, a board-certified veterinary oncologist at Southeast Veterinary Oncology and Internal Medicine in Orange Park, Florida. “When people’s hair grows, it just grows and grows and grows, so it’s always in antigen phase, but because a dog’s hair stops growing, those rapidly dividing cells are no longer dividing, and therefore they are no longer susceptible to chemotherapy.”

That said, there are some breeds of dogs whose hair does grow continually, and those dogs can experience hair thinning or total baldness from chemo treatments.

“I like to think about it as dogs that need a haircut to keep their look,” says Kim Ringen, DVM, a board-certified veterinary oncologist at Veterinary Referral Center of Colorado in Englewood, Colorado. “Those are the dogs who might see a thinning hair coat during chemotherapy. Dogs like Labs or Pugs, who do not need to go to the groomer to keep their look, don’t have fast-growing hair follicles, so they don’t lose their hair.”

Rodney Page, DVM, director of Colorado State University’s Flint Animal Cancer Center, who is board-certified in both internal medicine and oncology, tells me that certain chemotherapy agents can also change a pet’s skin color.

“The funniest experience I ever had was with a West Highland White Terrier that went completely bald and turned black,” Page says. “And then, as the chemotherapy was discontinued when he was in remission, all the white hair came back, but his skin remained hyperpigmented. In the meantime, he had a little mohawk that was preserved right down the middle of his head.”

Side note! Cats receiving chemotherapy lose their whiskers.

Why don’t pets feel as sick as people do?

Again, some do. Page explains that pets who’ve experienced gastrointestinal trouble before, or those who’ve ever had a bout with pancreatitis, are more likely than others to experience some vomiting or diarrhea from chemotherapy treatments.

Generally speaking, most pets don’t feel as sick because the doses they receive are smaller. “Across the board, per pound dosing schemes for dog and cat chemotherapy is about 50% of the dose people get,” Locke explains. “Usually, in those 10-15% that do have some affect, it’s pretty mild. They have a day of ‘I don’t feel like eating much’ or one episode of vomiting or diarrhea, then they are back to normal the next day. I’d say less than 5% of dogs have a significant toxicity.”

Page explains that it often isn’t as simple as doses based on a pet’s weight. With some drugs, doses are calculated based on the pet’s body surface area, in square meters.

“The example that I usually use is that you can have a 25-pound Dachshund, which is a long baloney thing, then you can have a 25-pound Whippet, which is essentially all bones and legs, so they are different, and they metabolize differently.”

What are the most common side-effects?

All chemotherapy drugs are different, but the most common possible side-effects include:

  • Nausea (may look more like excessive drooling)

  • Vomiting

  • Diarrhea

  • Lack of appetite

  • Change in activity level (which can sometimes signal a fever)

  • Secondary infections (usually in spots where the individual pet is prone to trouble – ears, skin, bladder)

Page recommends keeping a pets-only thermometer in the home and regularly checking a pet’s temperature so that you know what’s normal and what’s not – especially if a pet seems “off” after treatment.

The most watched possible side-effect is bone marrow suppression (red cells, white cells, platelets), which Page explains is why veterinary oncologists require regular blood work so that they can adjust doses and treatment schedules accordingly.

Each chemo drug has its own weird possible side-effect. For example, some can cause neurological issues that result in pets dragging their limbs.

Are any side-effects cumulative?

Some chemotherapies have the potential to cause problems with the heart, kidneys, liver, and bone marrow, but Ringen explains, “The majority of drugs we use in the canine world do not have a cumulative side-effect.”

There are some cases, where pets may take a daily pill form of chemo, where a pet can be totally fine for a long time, then suddenly experience side-effects.

“Most of the chronic toxicities in dogs are pretty well known,” Page says. “Our protocols are designed not to exceed the cumulative doses.”

In other words, there are limits to how much of certain drugs a pet can have in her lifetime. Once those limits are reached, veterinary oncologists will not give another dose.

Are people and other pets in the home at risk when a pet is receiving chemotherapy?

Most chemo drugs move through a pet’s system in 24-72 hours. As long as you clean up any eliminations carefully – wearing kitchen gloves or medical gloves when necessary to clean up messes - your exposure to chemo metabolites (what’s left after the body processes them) is low.

“There was an article published several years ago, trying to identify risks to people like me and my technicians who handle chemo and patients on a daily basis,” says Ringen. “That article illustrated that we actually have minimal risk as health care workers, that the majority of active chemotherapy properties are eliminated – broken down into inactive agents – by the time the patient is back in the clinic or in the home.”

That said, you want to avoid contact during the days following treatment with a pet’s:

  • Urine

  • Stool

  • Saliva

In other words, don’t let dogs who drool a lot kiss you or any kids in the household right after treatment.

“Some drugs are metabolized and still can be considered potential carcinogens in the urine or feces,” Page explains, “so the most vulnerable people in the household would be children, elderly people who are taking medications or are immunosupressed, others that are on those sorts of medications, and women that are pregnant. We are very careful that those individuals are not involved with cleaning up after the pet for 24-72 hours, depending upon the product.”

Frequent litterbox cleaning is recommended for multiple cat homes.

True or false: Chemo only buys a pet time?

“That’s a fallacy, so I’m throwing a flag on that one,” Locke says. “There are wide, wide, wide numbers of cancers – just like in people. Not all cancers are created equal. We have some cancers that are extraordinarily curable.”

There are some aggressive cancers, however, that are different:

Remember though that dogs and cats are different as well. “Osteosarcoma in dogs is often a death sentence, but for cats it’s completely different,” say Ringen, adding that surgery with clean margins in a cat can mean the kitty will live out his whole life.

The blood-centered cancers – leukemia, lymphoma – are a bit different. In many cases, the goal is remission, but often that remission can last years.

“With people, the big hallmarks of long-term remission are those five-year rates,” Locke explains. “So that five-year magic number in people, with dogs, because of their lifespan, is probably closer to a year, so if we can get dogs to a year, it’s like getting people to five years. Often when we get to the one, two, or three year mark after a cancer diagnosis, that’s where we start feeling like ‘Yes! We’ve truly cured this disease.’” Page lays out the numbers like this:

  • An estimated 50% of all dogs over the age of 10 will get cancer.

  • 50% of those can be cured with surgery or radiation.

“The other 50% fall into two categories: Ones for which we know we aren’t going to do much more than manage the pain and symptoms for a short period of time, then those types of cancer that are responsive to chemotherapy, responsive enough that it does significantly extend their survival time,” says Page, who calls the “buying time” theory a “glass-half-empty” attitude.

Can families ask for more aggressive chemotherapy doses?

The short answer is yes, but only if the pet proves she can handle it and if the risks of doing so are not too great. Page explains that veterinary oncologists are continually adjusting chemotherapy doses based on each individual pet’s medical history and tolerance for treatments. They don’t simply calculate the dose once and give that amount every single time.

It depends on the drug, however, since some chemotherapies have strict toxicity limits in pets. In those cases, Ringen says, “It would not be in the dog’s best interest to receive more than that dose because the side-effects are so much more significant than the benefit they would receive with a higher dose.”

Locke’s team often does ramp up doses in pets with no complicating factors. With osteosarcoma, for example, if a dog shows a good tolerance for treatment, and if a family is willing to be more aggressive, Locke will increase doses and add in drugs to combat possible vomiting and diarrhea.

Locke’s team also offers families the option of repeating chemotherapy for osteosarcoma in dogs six or eight months later. The initial chemotherapy plan is four total treatments in three-week intervals. If a dog continues to do well many months later, then she’ll recommend another two to four treatments.

What should I feed my pet who has been diagnosed with cancer?

“The role of diet in cancer prevention and cancer treatment is one of the hot button issues,” Locke says. “That’s probably one of the questions I field the most. And, ultimately, my response is this: ‘Exactly what you’ve been feeding him his entire life is fine.’”

While Locke was at Tufts University’s veterinary school completing her residency in oncology, she collaborated with a board-certified nutritionist there to study the oxidative and antioxidant status in dogs with lymphoma.

She says, “What we found was that they had imbalances of both their antioxidants and some of the vitamins in their systems when they were initially diagnosed, but by the time we got them into remission, those things had returned to normal levels pretty much on their own. So, it’s like the body is under some stress. No doubt about that, but when you get them into remission, then all of a sudden the body is able to adjust and get back to where it needs to be.”

What breakthrough would be a game-changer?

“I think if you asked anyone who treats cancer with dogs, hemangiosarcoma is the disease that’s the hardest one for everyone to manage and take care of,” Page says. “If there was a way to overcome that disease alone, we’d be jumping for joy.”

Why do pets handle chemo better than people do?

Currently a cancer patient herself, Ringen replies, “I do think there is a species difference. Even though all the organs are the same I do think there is a species difference … I think depression and anxiety play a bigger role in human cancer patients… The canine patient doesn’t comprehend statistics. They don’t have the anxiety about going in for tests. They don’t wonder if that test is going to be clean today. That really builds up, and they don’t have that… This is the lesson I’ve learned from my patients: Really live life to the fullest, and you tend to tolerate therapy because you’re not anxious about what’s going on.”