Is my dog at risk for cancer?

Yes, dogs are susceptible to many of the same cancers that affect people. For example, dogs are the only nonhuman species who can get prostate cancer. According to the National Cancer Institute, approximately six-million new cancer diagnoses are made in dogs each year. Since not all pets receive medical care or a definitive cancer diagnosis, this number would likely rise if every pet saw a veterinarian annually. Taking this into consideration, the Veterinary Cancer Society estimates one in four dogs will develop cancer at some point, and almost 50% of dogs over age 10 will develop cancer. Fortunately, half of all canine cancers are treatable if caught early enough, and new treatments and cures are continuously being researched.

What kinds of cancer are most common in dogs?

Cancer can take many forms and can affect the blood, bone, or body tissues. An accurate diagnosis is critical to provide the most appropriate treatment and the best prognosis. Dogs fall victim to the following types of canine cancers:

  • Lymphoma is one of the most common cancers seen in dogs, accounting for 20% of all canine cancers. Dogs are two to five times more likely than people to develop lymphoma, which can affect any breed at any age. Lymphoma appears most often as swollen lymph nodes under the jaw, in front of the shoulders, or behind the knees. Occasionally, lymphoma may attack lymph nodes in the chest or abdomen, which makes breathing difficult or causes vomiting and diarrhea. Lymphoma is generally considered treatable, depending on the type, and multidrug chemotherapy gives favorable results. Dogs who respond well to chemotherapy usually enjoy a good quality of life for the next 12 to 18 months of remission.

    Most commonly affected breed: golden retrievers

  • Mast cell tumors typically form on the skin, can vary from relatively benign to extremely aggressive, and often spread to other parts of the body. Mast cells are immune cells associated with allergies and are usually easily identified with a fine-needle aspirate. A pet suffering from a mast cell tumor will often show signs of vomiting, diarrhea, and loss of appetite. Surgery is required to excise the entire mast cell tumor, and chemotherapy and radiation therapy are often also indicated for the severe grades of tumor.

    Most commonly affected breeds: boxers and bulldogs
  • Osteosarcoma is the most common bone cancer in dogs, occurring most frequently in large and giant breeds. Osteosarcoma, which routinely attacks the long bones in the limbs but can affect any bone, progresses rapidly, spreading to the lungs, lymph nodes, and other bones. Pet owners notice swelling, lameness, or pain in the affected limb in the beginning stages. Since this disease is so aggressive and spreads extremely rapidly, amputation of the affected limb, followed by chemotherapy to treat metastases, is the recommended course of treatment. Sadly, fewer than 10% of dogs who undergo this gold-standard treatment live longer than three years.

    Most commonly affected breeds: Great Danes, Irish wolfhounds, mastiffs

  • Melanoma is one of the most common oral cancers seen in dogs and is frequently seen in breeds with dark tongues and gums. These tumors are composed of darkly pigmented cells and can be found anywhere on the body. A malignant melanoma that develops in the oral cavity has often spread throughout the body by the time it’s first noticed and, unfortunately, is incurable. Complete surgical removal is difficult, radiation therapy is ineffective against metastasized cells, and chemotherapy is ineffective against this type of cancer. Melanoma appears to respond to immune-based therapies, and several treatments are under development.

    Most commonly affected breeds: Doberman pinschers, standard and miniature schnauzers, chow chows, and Scottish terriers

  • Mammary gland carcinomas are the most common tumors in unspayed female dogs, but are often overlooked since they usually appear as a small nodule around a nipple. Unfortunately, the nodule may quickly grow into a large, painful tumor that can ulcerate and become an open wound. Approximately 50% of these tumors are malignant, but they can be cured with surgical removal if the cancer has not metastasized. Fifty percent of malignant masses will be fatal. Spaying a dog before her first heat cycle significantly decreases the mammary cancer risk.

    Most commonly affected breeds: older, unspayed females of every breed
  • Hemangiosarcoma is a form of cancer that develops from cells that line the blood vessels, most commonly attacking the spleen but also the liver, heart, and skin. Dogs with splenic tumors seldom display signs of illness until the tumor ruptures and they go into shock caused by extreme blood loss, with pale gums, sudden weakness, and labored breathing. Emergency surgery is required to stem the blood loss, followed by chemotherapy. Sadly, this disease rarely gives warning signals until it has progressed into the later stages and treatment is often too late.

    Most commonly affected breeds: golden retrievers, German shepherds, Portuguese water dogs, Skye terriers

What kind of signs should I watch for?

As with any disease, early detection is critical for the best outcome. Keep an eye out for these early warning signs of cancer in your dog:

  • Abnormal, and especially rapidly growing, swellings
  • Sores that do not heal
  • Loss of appetite and weight loss
  • Bleeding or discharge from body openings
  • Difficulty eating, swallowing, or breathing
  • Lameness
  • Difficulty urinating or defecating

While cancer is a terrifying diagnosis for your beloved pet, many new treatments look promising. Consider enrolling your pet in a clinical trial so her cancer diagnosis may lead to another pet’s cure. Familiarize yourself with what your veterinarian may be reading by referencing the 2016 AAHA Oncology Guidelines for Dogs and Cats.