YOUR DOG HAS CANCER … these are the words you least want to hear about your furry family member; however, the odds are you will hear them one day as a dog owner, especially if you have more than one dog in your lifetime.


Similar to humans, our pets are living longer due to advances in medicine and an emphasis on preventive care and nutrition. Living longer lives exposes our animals to diseases of aging, especially cancer. Much of what is known about canine cancer closely parallels what is known about cancer in humans. Treating cancer effectively and successfully is dependent upon the same variables found in human cancer treatment: type of cancer, the wisdom and experience of the attending doctor in choosing the effective course of treatment, the availability of advanced medical techniques, and the willingness and ability to pay for the treatment. An estimated six million dogs will be diagnosed with cancer this year. In many of these animals, the malignancy will look and behave much as it would in humans, i.e., spreading to the same organs.

Cancer occurs when the body’s immune system cannot stop cells from replicating at an abnormally fast, disorderly pace and forming a mass known as a tumor. Just as in humans, companion animal cancer is not caused by any single factor. While genetics and environmental factors can play a role in the disease’s development, other variables such as toxins, radiation and tumor viruses, as well as hormones can also be responsible for causing several types of cancer. Early detection is a critical factor. Cancer can be hereditary, sometimes running in the canine family for certain types of cancer. Variables like nutrition and toxic exposure seem to play a prominent role. Individual responses to the disease are also a factor, whereas, some dogs have immune systems that rally and have a good treatment outcome others may not. Additionally, treatment may be just a holding space for the inevitable and this is where the quality of life factor plays an integral role.


Make it a regular practice to examine your dog’s body for unexplained swelling or lumps.

Always have your trusted veterinarian aspirate (withdraw cells via thin needle) and, if necessary, biopsy (analyze the tissue sample under a microscope) lumps. Even benign growths should be carefully monitored for any changes.

Dogs are affected by more forms of cancer compared to other companion animals. According to The Veterinary Cancer Society, cancer is the leading cause of death in 47% of dogs, especially dogs over age 10. Dogs get cancer at about the same rate as humans. Some breeds or families of dogs have a higher incidence for developing cancer at an earlier age, but in most cases it’s a disease found in aging animals. There are nearly 100 types of animal cancer. Cancer in pets can be found in the skin, bones, breast, head and neck, lymph system, abdomen and testicles. Lymphoma, Hemangiosarcoma, and Mammary Gland cancer are the most common type of dog cancers.

Approximately one-third of all tumors in dogs are skin tumors, and up to 20% of those are mast cell tumors. The most common location to find mast cell tumors is the skin, followed by the spleen, liver, and bone marrow. Approximately half of all skin tumors are found on the body, another 40% on the limbs (most frequently the hind limbs), and the remainder on the head or neck. Approximately 11% occur in more than one location. The list below highlights the most common types of cancer.

  • Skin — Skin tumors are very common in older dogs. Most skin tumors in dogs are benign; some 20% are malignant or, rarely, become malignant over time. The appearance of these growths (lumps, cysts, growths, deposits, tumors) are a normal part of the aging process and it is important to watch them, and bring them to the attention of your veterinarian. Three common types: histiocytomas (button tumors)-raised, red, “buttons” of tissue is a benign tumor. Lipomas, or fatty tumors; and mast cell tumors, which are by far the most serious. Incredibly common especially in older dogs, it is important to have the tumor aspirated and the tissue observed under a microscope to ensure the tumor is benign. Always observe any changes that occur to diagnosed lipomas and report to your veterinarian any changes. Mast cell tumors are difficult to remove surgically, therefore, it is recommended to perform surgery and radiation/chemotherapy. If the tumor is “well-differentiated” meaning it is in a uniform appearance and not metastasized then the tumor can be successfully excised.
  • Hemangiosarcoma — A form of malignant cancer that arises from the cells that line blood vessels of various tissues of the body. This type of cancer is aggressive in nature, since its origin is in the blood vessels and often spreads to major organs of the dog. Hemangiosarcoma of the skin can be surgically removed and cured, provided there is not visceral involvement.
  • Mammary Gland (Breast) — 50% of all breast tumors in dogs are malignant. Spaying your female dog before 12 months of age (or first heat) will greatly reduce the risk of mammary gland cancer. Average age of onset is 10 years or older. If caught early and the tumor is still localized there is high probability it can be cured; however, if the cancer has spread, the treatment hinges on quality of life issues versus possible cures.
  • Head & Neck — Neoplasia of the mouth is common in dogs. Signs to watch for are a mass or tumor on the gums, bleeding, odor, or difficulty eating. Since many swellings are malignant, early, aggressive treatment is essential. Neoplasia may also develop inside the nose of dogs. Bleeding from the nose, breathing difficulty, or facial swelling are signs that may indicate neoplasia and should be checked by your veterinarian.
  • Lymphoma — Lymphoma is a common form of neoplasia in dogs. It is characterized by enlargement of one or many lymph nodes in the body. Basically, it is cancer of the blood cells and tissues associated with the lymphatic system. Generally afflicting middle-aged and older dogs, it responds well to chemotherapy. Unfortunately, there is a high incidence of relapse.
  • Testicles — Testicular tumors are common in dogs, especially those with retained testicles (testicles that did not move to their normal positions during growth, and may be located in the abdomen or between the abdomen and scrotum).
  • Bone — Bone tumors are most often seen in large breed dogs and dogs older than seven years. The leg bones, near joints, are the most common sites. Persistent pain, lameness and swelling in the affected area are common signs of the disease.

Emotions run high when we humans hear the word “cancer.” Should your veterinarian suspect cancer in your pet, the first step is to obtain a definitive diagnosis, develop a treatment plan along with your vet or veterinary specialist and prepare to be an advocate for your pet by arming yourself with information.

Other useful links:

Animal Cancer Foundation

National Canine Cancer Foundation

Dog Cancer blog

PetCure Oncology

Arizona Veterinary Oncology

Charlie’s Doggie Bag