Pet Care

Signs and Symptoms of Cancer in Pets

Signs and Symptoms of Cancer in Pets

Did you know that both cats and dogs have a 50% chance of getting cancer by ten years old? As a pet owner, feline and canine cancer is a very common health concern for your furry friend. However, we have some good news—the earlier you catch cancer, the more likely you can keep your pet healthy.

So, how to catch the "Big C" before it affects your pet? It all starts with identifying the most common cancer symptoms in dogs and cats. Catching cancer early on allows your pet to receive the treatment option it needs to prevent cancer in dogs or slow metastasis—when cancer spreads to multiple parts of the body.

#1 Lumps, Bumps, and Growths

You're scratching your pooch or kitten on the back, when all of a sudden….oh no, what's that?

If you notice a new bump or lump on your pet's body, don't immediately panic. Not all new masses are cancerous. However, many cancers do lead to new masses—so inspection and veterinary guidance are crucial.

When discussing cancer, a "lump" is usually shorthand for a tumor. Tumors are masses of tissue created by cells growing at an abnormally fast rate. Tumors can be benign (free of cancer) or malignant (cancerous).

For a pet parent, it can be difficult to tell whether your pet's bump is just a skin tag or something more dangerous. Keep a lookout for any signs of these common malignant tumors in dogs and cats:

  • Mast cell tumor – Mast cells are a type of white blood cell that can turn cancerous in both cats and dogs. Mast cell tumors often lie right underneath the skin, appearing hairless, pink or red, raised, and itchy for your pet. Luckily, mast cell tumors are easily removed with surgery when caught early.
  • Melanoma – When skin pigment cells called melanocytes become cancerous, they form melanoma tumors. These masses often appear in the mouth or toes of pets as dark patches of skin. It's especially important to catch melanoma early since it metastasizes quickly.
  • Squamous cell carcinoma (SCC) – Cancer in cats symptoms may include this type of skin cancer that usually appears in and around the mouth. In dogs, SCC usually appears in light-skinned areas like the underbelly, toes, or mouth. These tumors are usually pink, scabby, and small, and they have an irregular and hardened border.
  • Fibrosarcoma – Like the "fibers" of skin, fibrosarcomas originate in the connective tissues right below the skin surface. Older pets have a much higher likelihood of developing fibrosarcomas. Their appearance can range from single to multiple, semi-firm to firm, or closed to ruptured. However, they often grow larger with time.
  • Swollen lymph nodes – While not technically a tumor, swollen lymph nodes are definitely a lumpy sign that your older dog or cat is sick—and possibly has lymphoma. The multicentric variant of this cancer can swell your pet's lymph nodes up to ten times their normal size. Dogs are especially prone to multicentric lymphoma.

#2 Foul odors

When Googling "what are the symptoms of cancer in dogs and cats," you probably wouldn't expect odors to top the list. However, that stinky breath may not just be your pet's natural state. Newly foul odors are a common symptom of cancer.

In other words—if you smelt it, it should be dealt with.

Smelly odors are usually a symptom of oral cancers. Any type of cancer that originates from or spreads to the oral cavity could affect your pet's breath, leaving behind a strong (and often nasty) smell. However, cancer-related odors can also originate in the nose or anus.

If you notice a freshly foul smell coming from your pet, it might be a sign of the following cancers:

  • Melanoma, or cancer of skin pigment cells
  • Squamous cell carcinoma, or cancer of skin cells
  • Fibrosarcoma, or cancer of connective tissues
  • Adenocarcinomas, or cancer of the glands that line inner organs (like the anus)
  • Osteosarcomas, or cancer of bone growth cells

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#3 Slow-Healing Wounds or Sores

You know how when you're sick, your scabs or hangnails take forever to heal? Well, the same is true for your furry friend. Wounds or sores that stick around may be (literal) red flags that a serious condition is afoot—like cancer.

Slow-healing wounds can occur with cancer for two reasons:

  • Ulcers – Some forms of malignant tumors may ulcerate or rupture, creating wounds on the skin's surface. This is especially true for skin cancers like melanoma or hemangiosarcoma.
  • Immunity support – Cancer is an incredibly taxing condition on your pet's immune system. Without enough energy, their body may not be able to repair any benign or everyday wounds as quickly.

#4 Loss of Appetite & Weight Loss

No, they're not on a new fad diet. If your dog or cat suddenly stops chowing down on dinner, it's definitely a sign that something's off with their health.

A loss of appetite is usually one of the first signs of cancer, particularly for cats. Unfortunately, this symptom is doubly-dangerous for your pet. The more they don't eat, the more weight they may lose—a recipe for low strength and a weaker immune system. A veterinarian can help form a plan to stimulate your pet's appetite and increase its caloric intake during cancer treatment.

#5 Digestive Distress

Many forms of cancer can cause digestive distress in pets, particularly those that originate in the gastrointestinal system or internal organs (including the stomach, intestines, spleen, and liver).

Symptoms of dog cancer and cat cancer may include:

  • Nausea – While hard to detect, nausea is a common cancer symptom in pets. This could appear as discomfort, expressions of pain, passing gas, or a refusal to eat.
  • Vomiting – Not your average hairball hack or post-garbage-can-rummage hurl? Consistent or violent vomiting is a possible sign of internal cancer. If your pet vomits more than twice per day, vomits blood, or constantly attempts to throw up, then it's worth getting a veterinary opinion.
  • Diarrhea – Occasional diarrhea is normal for all pets. But routinely loose or uncontrolled bowels are a sign of digestive disturbance that could be cancer-related.
  • Bloody fecal matter – Red or black blood in your pet's stool is an immediate red flag. Black stool often means the blood dried in your pet's digestive tract before it was excreted.
  • Stomach swelling – If they're looking a little more like Pooh Bear than normal, it might be a sign of internal cancer. Certain tumors can leave the stomach very swollen and tight.

#6 Seizures

Seizures are a scary event for both pets and their parents. Also known as idiopathic epilepsy, these uncontrolled fits are a sign of brain tumors in both cats and dogs. While it may seem obvious, you should always consult veterinary care if your pet experiences a seizure.

Depending on the severity and affected area, seizures in dogs or cats can present as follows:

  • Sudden and uncontrolled movements
  • Jerking limbs
  • Foaming at the mouth
  • Losing consciousness
  • Sudden rage or hysteria
  • Excessive biting or scratching

#7 Urinary Symptoms

All of a sudden, your pet is having a lot more accidents—like, a lot. If you notice that your pet can't control its bathroom needs, it's probably not a rebellious phase. Urinary issues are a common sign of transitional cell carcinoma, cancer that originates in the bladder. This may leave your older dog or cat with the following:

  • Frequent and small urination
  • Painful urination
  • Bloody urine
  • Incontinence

#8 Depression, Fatigue, and Low Energy

As a pet parent, there's nothing worse than seeing your little one upset. If your once-happy furry friend suddenly seems down in the dumps, it could be more than a mood swing. Depression and low energy are common signs of cancer, especially during the early stages.

Keep an eye out for long-term shifts in your pet's mood, such as:

  • Disinterest in normal playtime and activities
  • Antisocial behavior with other animals
  • Excessive hiding
  • Oversleeping
  • Slow movements
  • Reluctance to move or exercise
  • Excessive anxiety with new people or surrounding

#9 Respiratory Issues

If five minutes of playtime leaves your pup or kitten wheezing, they might not need an exercise program. New respiratory symptoms could be a sign of cancer spreading into the lungs, throat, or nasal cavities. While lung cancer is quite rare for both dogs and cats, tumors in nearby tissues (like the chest) may leave them with respiratory issues like:

  • Coughing
  • Difficulty breathing or heavy breathing
  • High-pitched or wheezing noises
  • Chronic nasal discharge
  • Difficulty breathing
  • Pitch change in voice

Tell Pet Cancer "No" with Papaya

Whether you're caring for a healthy puppy or an old feline, it's never too late to protect your four-legged friend from cancer by educating yourself on what to look out for, such as lumps, foul odors, the types of cancer in dogs, or digestive issues.

If signs do arise, Papaya Veterinary Pet Care is here to lend a guiding hand to answer questions like what causes cancer in cats and dogs.

As veterinarians, our goal is to make your pet feel safe and soothed. That's why when your pet walks through our doors, they feel happy to be here. And for the pet parents, we provide equal reassurance. Our expert team offers primary, preventative, telehealth, and pet clinic emergency care services so that your best friend always receives the care they need.

Cancer is a scary diagnosis for pets—but with affordable vet care using a Papaya Pet membership, their treatment is facilitated by caring professionals that make each visit a treat.


  1. American Kennel Club. Lymphoma in Dogs: Symptoms, Diagnosis, and Treatment.
  2. American Kennel Club. Dog Skin Cancer: Types, Symptoms, and Treatment.
  3. Chaska Valley Veterinary Clinic. 10 Symptoms of Cancer Every Pet Owner Should Know.
  4. Embrace Pet Insurance. Canine Lumps and Bumps: Superficial Tumors on Dogs.
  5. Merck Veterinary Manual. Cancers and Tumors of the Lung and Airway in Cats.
  6. Reader's Digest. 11 Warning Signs of Cancer in Cats That Every Owner Should Know.
  7. Spring House Animal Hospital. Types of Tumors Seen In Dogs & How They Are Treated.


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