Skin Cancer in Dogs

Skin cancer in dogs includes out of control growth of the skin cells, whether associated with hair follicles, glands, fat or connective tissue. Cancer can spread to the skin from other parts of the body, but since these cancers did not originate in the skin, they are not technically considered skin cancers. Skin cancer is the most common type of dog cancer.

Causes of Canine Skin Cancer

Some types of skin cancer occur in dogs for reasons that vets don't understand. However, it's believed that overexposure to the sun causes at least two types of skin cancer, squamous cell carcinoma and hemangioma. Light colored dogs and dogs with thin fur have a higher risk of developing these types of cancers. Skin cancer occurs most often in dogs 6 to 14 years of age, though there are some skin cancers that occur primarily in younger animals.

Some breeds of dog may be predisposed to develop skin cancer. They include:

  • Boxers
  • Basset Hounds
  • Scottish Terriers

Types of Skin Cancer

There are four types of canine skin cancer, classed according to which type of skin cell is involved. They are:

  • Round cell tumors, which include lymphosarcoma, mast cell tumors, histiocytomas, plasma cell tumors and transmissible venereal tumors.
  • Epithelial tumors, which are tumors of the skin itself, its glands and its follicles.
  • Melanomas, which are tumors that occur in melanocytes, or skin cells that create pigment.
  • Mesenchymal tumors, which grow in the fatty cells, membranes, blood vessels and nerves in and around the skin.

Lipomas and papillomas, or cancerous warts, are two of the most common types of dog skin cancer. Lipomas are fatty deposits that occur under the skin and often remain benign, or non-cancerous. Your dog may also develop papillomas that do not become cancerous.

Canine mast cell tumors are also common, and may appear on the skin or in organs like the intestines. Sebaceous gland tumors are small lesions that may secrete a discharge that becomes crusty.

Symptoms and Diagnosis of Skin Cancer in Dogs

If your dog has a lump under his skin that begins to grow larger, it may be skin cancer. Sores that never heal, and may bleed or itch, could be cancerous. Moles and warts that become discolored, begin to grow, bleed or itch could be skin cancer.

Your vet will perform some of these tests to verify skin cancer:

  • Cytology, or microscopic examination of cells from the tumor.
  • Biopsy, a procedure in which the vet takes a sample of cells from the tumor in order to examine them.
  • Complete blood count
  • Serum chemistry panel
  • Urinalysis
  • X-rays

Treating Canine Skin Cancer

Treatment options for skin cancer in dogs vary depending on the type of tumor and its size at the time of diagnosis. Surgery may be an option if the cancer has not yet advanced and the entire tumor can still be removed, or to reduce a tumor's size to make further treatment more effective. Radiation therapy may be used on tumors that cannot be entirely removed. Chemotherapy is used on tumors that have already spread.

Cryosurgery is a procedure used on small tumors. In cryosurgery, the tumor is frozen and removed. A newer form of skin cancer treatment, photodynamic therapy, uses an injectable dye to locate cancer cells. The cells are then killed with a laser.