Cancer in Dogs: Signs, Diagnosis and Treatment

Cancer in dogs can be a scary diagnosis, but it doesn’t always mean the worst. Just ask Joshua Lachowicz, DVM, DACVIM (Oncology), and medical director at BluePearl Veterinary Partners in Queens, New York.

“I adopted a dog that had stage 5 lymphoma,” Dr. Lachowicz recalls. “I thought he would probably have six months to live based on his profiles. But he ended up going into remission after six weeks of chemotherapy—and he lived on for three years! He was on and off chemo, but it was five times as long as I thought I’d have with him based on what was supposed to happen by the book.”

If your beloved dog has been diagnosed with the disease, it can be a time filled with uncertainty and fear—but it’s not without hope. Below, we’ve outlined what you need to know to prepare yourself and your pal for battle against cancer in dogs.

“It’s always good to get the facts, know what you’re dealing with, and know that there’s hope, because there’s always something on the horizon,” Dr. Lachowicz says.

Can Dogs Get Cancer?

Like humans, dogs can get cancer. They can develop both benign and malignant types of tumors, says Kelly R. Hume, DVM, DACVIM (Oncology), associate professor of oncology at Cornell University College of Veterinary Medicine in Ithaca, New York.

“Overall, dogs are prone to a variety of skin tumors, both benign and malignant,” she says. “Another type of cancer in dogs that veterinary oncologists treat commonly is called lymphoma—this is a malignant cancer of lymph nodes. Large breed dogs are particularly susceptible to bone cancer.”

In the United States, those types—skin tumors, lymphoma and bone cancer—are indeed the “big three,” says Timothy M. Fan, Ph.D., DVM, DACVIM (Oncology), professor with the department of veterinary clinical medicine at the University of Illinois at Urbana-Champaign and president of the Veterinary Cancer Society. “The ones we mostly see are lymphoma, mast cell tumors [of the skin] and osteosarcoma,” aka bone cancer, he says.

It’s possible, however, for dogs to develop cancer in any organ or tissue in the body, says Dr. Lachowicz. In fact, in its Oncology Guidelines for Dogs and Cats, the American Animal Hospital Association notes eight common cancers in dogs:

1. Anal sac carcinoma
2. Lymphoma
3. Mammary gland cancer
4. Mast cell tumor
5. Oral malignant melanoma
6. Osteosarcoma
7. Soft tissue sarcoma
8. Splenic hemangiosarcoma

“We do see a fair bit of other tumors, like mammary gland carcinoma and pulmonary, or lung, carcinoma, and then quite a few head and neck tumors, including different types of oral tumors,” Dr. Lachowicz says.

What Causes Cancer in Dogs?

Though it’s difficult, if not impossible, to pinpoint a specific cause for cancer in dogs, experts say that the genetic disease is a result of mutations that occur in the cell’s DNA.

“Different types of cancer are caused by different things,” Dr. Hume says. “For most cancers in individual patients, we don’t know exactly what caused the cancer to develop. We know that mutations occurred in the cells that have caused them to replicate uncontrollably, but we don’t necessarily know why those mutations occurred in the first place.”

Sometimes the mutation is from random chance, sometimes it’s from an environmental trigger, and sometimes it’s inherited, she says.

When the disease manifests spontaneously, Dr. Lachowicz says, it can be triggered by chronic inflammation or environmental factors.

“Cigarette smoke, for example, can be a carcinogen that can increase the risk for developing lymphoma and lung cancer,” he says. “People oftentimes blame diet, but diet doesn’t usually lead to cancer unless it is causing inflammatory changes, which then sets the stage for cancer.”

Other environmental triggers, like exposure to radiation and chemicals—pesticides, fungicides, herbicides—can increase a dog’s risk for lymphoma, Dr. Lachowicz says. They can also be genetically predisposed to developing cancer, too.

“Just like with humans, if someone has the BRCA mutation, they’re at a higher risk for breast cancer,” Dr. Lachowicz says. “Unfortunately, even with the canine genome fully mapped, we don’t have a lot of great genetic information about cancers at this point, although that will come down the road.”

Certain types of endocrine diseases can also make dogs more susceptible to cancer, he says.

“For instance, dogs with low thyroid might be more prone to developing thyroid cancer,” Dr. Lachowicz says. “So, it could be even linked to certain internal diseases. There’s a long list, and even with an individual patient, it’s almost impossible to say what caused the cancer.”

Signs of Cancer in Dogs

The signs of cancer in dogs vary depending on the type of cancer and how advanced it is, but Dr. Hume and Dr. Lachowicz point to three key indicators:

1. Strange lumps or bumps, like swollen lymph nodes under the neck or groin, or lumps under the skin
2. Vague signs of illness, such as decreased appetite or weight loss, coughing or sneezing, vomiting or diarrhea, or difficulty urinating
3. Abnormal behavioral changes, like limping, lameness, lethargy or reduced activity, particularly in younger dogs

Remember that these are only general signs of cancer in dogs, notes Dr. Lachowicz.

“The list of symptoms goes on and on,” he says. “But for the non-specific signs, it’s loss of energy, loss of appetite, weight loss, not doing the normal routine.

“And then the specific signs can be anything from respiratory issues, like coughing, sneezing, nasal discharge; to the gastrointestinal issues, like vomiting, diarrhea, loss of appetite, weight loss; to lameness if it’s a bone tumor; to lumps and bumps if it’s a skin tumor,” he continues.

Cancer in dogs is a complex issue, Dr. Lachowicz says, so it’s critical to keep the lines of communication with your veterinarian open.

“Any sign or symptom that is out of the ordinary and progressive needs to be evaluated, whether it’s an older pet or a younger pet,” he says. “Every pet is going to be entitled to a one-off, just like you and I would be, but anything that’s more progressive or unexpected should be evaluated.”

Diagnosing Cancer in Dogs

To diagnose cancer in dogs, veterinary oncologists first perform a cellular analysis (cytology) or a tissue biopsy (histopathology) of the tumor, Dr. Hume says.

“To know if an abnormality is cancerous, the cancerous tissue has to be examined under a microscope,” she says. “This can be done by looking at cells obtained from a needle aspiration, or by looking at a piece of tissue, usually collected via a biopsy or surgical procedure.”

“Sometimes cancer is strongly suspected based on the results of diagnostic imaging, such as with radiographs (X-rays), ultrasound (sonogram) or CT of an abnormal area in the body,” Dr. Hume adds.

Abnormal bloodwork might reveal a blood cancer, like leukemia, but most cancers do not show up in the bloodstream, Dr. Lachowicz says.

“That said, bloodwork does sometimes give us hints to follow after for certain things,” he says. “For instance, if an animal is anemic, why are they anemic? Could that be related to cancer? Why are the patient’s liver values elevated? Could that be linked to cancer?”

How to Treat Cancer in Dogs

If the veterinarian detects a malignant tumor, dog cancer treatment is the next step. Therapies mirror those of human cancer patients: surgery, chemotherapy, radiation therapy, molecular targeted therapy and immunotherapy, Dr. Hume says, along with palliative therapy and symptomatic care.

Most dogs, however, are treated with surgery, radiation and chemotherapy, or a combination thereof, Dr. Lachowicz says.

“You either cut out the tumor, irradiate the tumor, or if you can’t get all the cancer out of a particular area, you can do radiation on the cells left behind,” he says. “And then chemotherapy is used either for liquid types of cancers like lymphoma, in conjunction with surgery, or for cases where it’s a high-grade tumor from a very aggressive type of cancer, like hemangiosarcoma, which is cancer of the [blood vessel walls and commonly affects the] spleen.”

Oncologists also use drugs like NSAIDs (nonsteroidal anti-inflammatory drugs) and immunotherapy—using the body’s own immune system to fight cancer—for dog cancer treatment.

“Researchers are working constantly to develop more effective, safer therapies for veterinary patients as well as human patients,” Dr. Hume says.

How to Prevent Cancer in Dogs

Can cancer in dogs be prevented? No, says Dr. Fan, but the risk can be reduced.

“We don’t know anything about how to prevent these tumors because there isn’t a singular underlying cause for it that we know of,” he says. “For any type of cancer, there are multiple factors that promote or lead to susceptibility and there’s not a singular thing that you should be doing to prevent it.”

To reduce the risk of cancer, Dr. Hume recommends regular exercise, a well-balanced diet, avoiding secondhand smoke exposure and obtaining regular health care.

“And there may be specific risk reduction strategies for specific breeds, so if your dog is a breed that is at risk for a specific cancer type, you should discuss with your veterinarian whether any specific strategies are recommended,” she says.

Dr. Lachowicz recommends spaying and neutering your dog at an early age, too, to prevent testicular or ovarian tumors. Early spaying can help prevent mammary tumors, too, he says.

“Mammary tumors are more common in dogs that have gone through multiple heat cycles,” he says. “If they’re spayed before they go into heat, that lowers their risk of developing mammary tumors.”

And if your four-legged pal likes to sunbathe—particularly if they have a thin coat of fur—consider covering their skin with dog-safe sunscreen or a T-shirt, Dr. Lachowicz says.

“The vast majority of skin tumors are not going to be environmentally linked from sunlight and UV exposure, but there are some exceptions to that,” he says. “If you have a dog that doesn’t have a lot of fur protection that likes to go out in the back and roll in the grass and lay there for a while, you might want to protect the skin surface or limit their sun exposure.”

As for a dog cancer diet, Dr. Lachowicz says that pets battling the disease should keep off the carbs.

“Animals with cancer should be fed a high fat and high protein diet, and one limited in carbohydrates, assuming there are no contraindications,” he says. “Cancer cells feed off of carbs but have a more difficult time utilizing fats and proteins.” But don’t implement a dog cancer diet without consulting an expert, Dr. Lachowicz advises: “Before changing your pet’s diet, always check with your veterinarian first.”

Learn more about dog cancer diets.

Of course, the best way to reduce your dog’s cancer risk is to regularly visit the veterinarian, say experts.

“Early detection is super important,” Dr. Lachowicz says. “We need to make sure our pets are examined by a veterinarian annually. Once they get to 4, 5, 6 years of age, they should be seen every six months. The exam should include routine testing, routine blood test, urine test, maybe even an X-ray here and there to make sure everything looks OK before cancer strikes.”

And if cancer does strike, seek the advice of experts who are well-versed in oncology, Dr. Fan says.

“It never hurts to ask for a second opinion from a boarded veterinary oncologist, people who deal with this every day, to get the best information,” he says.

Common Questions about Cancer in Dogs