Skin Cancer in Dogs

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Overview of Canine Skin Cancer

Skin cancer encompasses a broad category of tumors that includes any uncontrolled growth of cells of the skin or associated structures such as glands, hair follicles and supportive tissues (fat and connective tissue). Metastasis to the skin from tumors elsewhere in the body can occur but these are not considered skin tumors because they did not start in the skin.

The skin is the most common site of cancer in the dog and the second most common site of cancer in the cat. Dogs have up to six times the number of skin tumors as cats; however, skin tumors in dogs are more likely to be benign than those in cats. Skin cancer frequently occurs in dogs that are middle-aged to older (six to 14 years of age), although there are several types of skin cancers that occur in young animals.

Breeds of dogs that have been found to have a higher incidence of skin cancer include boxers, Scottish terriers, bull mastiffs, Basset hounds, Weimaraners, Kerry blue terriers and Norwegian elkhounds.

The cause of most skin cancers is unknown. Exposure to the sun has been shown to cause a higher incidence of two types of skin cancer: squamous cell carcinoma and hemangioma. Light-colored dogs with thin haircoats that spend time in the sun have a higher risk of developing either squamous cell carcinoma or hemangioma. There may be a genetic basis for the development of certain cancers.

Skin cancers can be divided into four categories, depending upon the cell type that is involved. These categories are epithelial tumors, mesenchymal tumors, round cell tumors and melanomas.

  • Epithelial tumors. These tumors involve the skin itself, glands in the skin or the hair follicles.
  • Mesenchymal tumors. These tumors are derived from cells that surround or support the skin such as fat, connective tissue, blood vessels and nerves.
  • Round cell tumors. These tumors are named because of their appearance under the microscope and include lymphosarcoma, mast cell tumors, histiocytomas, plasma cell tumors and transmissable venereal tumors.
  • melanomas. These tumors are derived from melanocytes – cells that provide pigment in the skin.

    In dogs, the most common tumors are lipomas, mast cell tumors, sebaceous gland adenomas/hyperplasia and papillomas. Most skin cancers appear as a lump in or underneath the skin or as a sore that does not heal. Animals with skin cancer may experience discomfort or itchiness because of the cancer. This may cause them to chew or scratch at the affected area. With certain types of cancer, there may also be redness to the skin or it may have a flaky appearance.

  • Diagnosis of Skin Cancer in Dogs

    Diagnostic tests are needed to recognize skin cancer and exclude other diseases in dogs. The ability to treat a skin cancer successfully depends upon the type of cancer and how advanced it is at the time of diagnosis. Tests that your veterinarian may wish to perform include:

  • Cytology, which is microscopic examination of cells obtained from an aspirate of the tumor or a biopsy
  • Biopsy, which is removal of portion of the tumor so that it can be evaluated cytologically or with histopathology, in which the tissue is fixed and then sectioned prior to examination under a microscope
  • Complete blood count (CBC)
  • Serum chemistry panel
  • Urinalysis
  • Chest radiographs (X-rays)to determine if the tumor has spread to the lungs
  • Treatment of Skin Cancer in Dogs

    Treatment for skin cancer depends on the type of tumor that is present and how advanced the disease is at the time of diagnosis.

  • Surgery may be performed if the tumor has not spread and the entire tumor can be removed without compromising function of the associated tissues. Occasionally it is used to reduce the size of a tumor so that other treatment can be more successful.
  • Radiation therapy may be considered for some tumors, particularly when the entire tumor cannot be removed surgically.
  • Chemotherapy may be considered for some types of tumors, particularly for those that have spread to other tissues.
  • Cryosurgery is a procedure where the tumor and adjacent skin are frozen. It is generally considered for use only with small tumors.
  • Photodynamic therapy is a new treatment modality that uses a dye injected into the blood stream that localizes in cancer cells. A laser of a particular wavelength is then used to excite the cells and cause cell death.
  • Home Care and Prevention

    Examine your dog’s skin on a regular basis. If you note a new lump, a sore that does not appear to heal, or other changes in the skin seek veterinary attention as soon as possible.

    After surgery monitor the incision for redness, swelling or discharge. Alert your veterinarian if any of these signs are noted.

    Avoid prolonged exposure of your dog to sunlight. This is particularly important if your dog has light colored skin.

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