Common Cancers in the Dog and Cat

No one likes to hear the word cancer.  Unfortunately, just as with people as we age, cancer becomes a concern for our pets as well.  Cancer is now the most common natural cause of death in dogs and cats.  Below is a list of common cancers, the breeds they affect most, and a little about each one.

If your dog or cat exhibits any of the following symptoms, he or she needs to be seen by a veterinarian.  The most common symptoms we see in cancer patients are:
  • Any new skin masses or swellings that look abnormal or are rapidly growing
  • A decrease in appetite
  • Weight loss
  • Exercise intolerance or loss of energy
  • Persistent lameness
  • Difficulty breathing, persistent cough or fast respiratory rate

Skin Cancers

As pets age, it is common to get little cysts and benign skin tumors.  Most of these have a very characteristic look to a veterinarian, but getting an aspirate of the mass and looking at the cells under a microscope is the best way to give you a diagnosis.  Here is a list of some of the most common skin cancers:

Benign Skin Tumors
  • Lipoma - This is a fatty tumor that is present under the skin and is easily moved around underneath the skin.   We remove these if they grow rapidly or are in a location that is causing discomfort (such as over a joint).
  • Sebaceous cyst - This is a cyst filled with thick debris that almost looks like toothpaste when it is expressed.  This is just a cyst that got plugged.  Removal is curative.
  • Sebaceous adenoma - This is a skin tumor that looks like a wart and has a cauliflower appearance.  Sometimes there is a scab associated with this tumor.  Removal is curative.
  • Histiocytoma - This is a cherry red, small, round skin tumor in young dogs that arises suddenly.  These masses will go away over time, but if they are in a location that is uncomfortable then they can be removed.
  • Basal cell tumors - These are more common in cats, and like to grow on the tips of the ears and around the neck.  They are firm round masses in the skin.  Removal is curative.

Malignant Skin Tumors
  • Mast Cell Tumors - These tumors can range in size and shape and can be darkly pigmented or the normal skin color.  Often these will come up very suddenly and can get bigger and smaller quickly (this is because these tumors secrete histamine, which is responsible for symptoms in allergic reactions).  They can be slow or quick to spread so wide surgical excision of the mass is  recommended as early as possible.  Boxers, Golden Retrievers and Bernese Mountain Dogs are highly predisposed.
  • Melanoma - These are darkly pigmented skin tumors that can be quite aggressive.  Usually solitary skin lesions are slow to metastasize but those found on mucocutaneous junctions (lips, gums, eyes, anus) and in between the toes are usually highly malignant.  There is a vaccine available for melanoma once it is diagnosed and must be given by a veterinary oncologist.
  • Lymphoma - Though rarer than other forms of this cancer, lymphoma can occur in the skin.  When it does it is termed "mycosis fungoides" because it often mimics deep infections that do not respond to antibiotics or other medications.  A biopsy is usually needed to diagnose it.   
  • Squamous Cell Carcinoma - This skin tumor commonly occurs on the face and ears of cats, and also on non-pigmented areas of light colored dogs such as the ears and around the eyes.  This tumor will become ulcerated and very locally invasive.  Wide surgical excision is needed to remove the tumor, but in a lot of cases this is not possible because of the location of the tumor.

Other Common Tumors We See

  • Meibomian gland adenoma - If your dog or cat has a small pigmented mass growing out of the eyelid do not be overly concerned; this is likely a benign tumor called a meibomian gland adenoma.  The meibomian glands secrete the substances that keep the eye moist.  Removal is curative but more tumors can arise at any time.  
  • Mammary tumors - These tumors arise in older dogs and cats and feel like hard nodules within the mammary tissue.  These tumors can spread rapidly to the lungs so removing them quickly is ideal.  Intact female dogs and cats are at greater risk, so spaying your pet before her first heat cycle will greatly reduce the risk of developing mammary cancer.  In addition, if your pet is not spayed and has developed mammary cancer, then this surgery needs to be done at the time of the tumor removal because without spaying, these tumors will keep growing.
  • Transitional Cell Carcinoma - This is the most common tumor in the bladder.  Dogs and cats are evaluated for these tumors if they have a history of chronic urinary tract infections or bloody urine.  Medication can treat these cancers quite well and can even put them into remission for some time.  About 30% of these tumors will spread to the lungs without treatment, and even in some cases with treatment.
  • Osteosarcoma - This is a tumor of the bones that causes lameness and painful swellings, most often around the knee and on the shoulder of large breed dogs.  A bone biopsy and x-rays are usually needed to make a diagnosis.  Treatment is usually by amputation of the affected limb and chemotherapy.  Amputation is done solely to remove pain and not to cure the cancer.  Most dogs survive about 4-5 months after diagnosis.
  • Hemangiosarcoma - This tumor arises from blood vessels and can occur anywhere in the body.  The most frequent places are on the spleen, liver and skin.  Skin tumors will bleed easily.  If tumors are on the spleen or liver, often times there are no clinical signs until the cancer is very advanced, and then can include lethargy, weakness, anemia, vomiting and abdominal enlargement.  Treatment can include removal of the spleen and supportive care, but most of these dogs succumb to their cancer within months.  
  • Lymphoma (intestinal or systemic) - Intestinal lymphoma is more common in cats and can cause vomiting, diarrhea, weight loss, or reluctance to eat.  With chemotherapy, most cats live 3-6 months or more after diagnosis.  Systemic lymphoma is more common in dogs and will result in lymph node swellings throughout the body.  With chemotherapy, most dogs live 6-12 months after diagnosis.

Can Cancer Be Preventable?

Just as with people, there is no hard evidence to point to diet or lifestyle as a cause of cancer.  We know that some breeds or species are predisposed to getting certain types of tumors, and diligence with these breeds as they age is a good way of catching cancer early.  There are some recommendations, however, to help keep your pet as healthy as possible and hopefully decrease their chances of getting not only cancer but other common disorders as well.
  • Keep your pet lean and active - A good body condition means your pet is in top physical shape.  This will help in all aspects of their life.  Feed a good quality diet appropriate for your pet's life stage and maintain plenty of exercise.
  • Omega 3 fatty acids - Adding a fatty acid supplement into your pet's diet may help prevent cancer, though this is not a proven fact.  Fatty acids will also help with coat quality, may improve allergies, and may help slow the progression of arthritis.
  • Spay and neuter your pets - Intact animals have a much higher risk of getting cancers (ovarian, uterine, mammary, testicular and prostate) than spayed or neutered pets.  Even if you have an adult  dog who has been bred and now is retired, it is never too late to spay or neuter!
  • Do not smoke around your pet - Just like the recommendations for people, being around these carcinogens may cause cancers in pets too.
  • Be diligent about skin tumors or other clinical signs - if your pet has any skin tumors or is acting out of character in any way, consider bringing him or her to the vet for a checkup.  We can aspirate skin masses, perform bloodwork and x-rays and even send out a blood test for cancer markers if we are suspicious of internal disease.  Early diagnosis and treatment will give you the best outcome for you and your pet.