What are skin tumors?
Skin is the outer layer of animals' body that is made up of multiple layers of epithelial tissues that guard underlying muscles
and organs against damage. Many types of skin tumors, both benign (noncancerous) and malignant (cancerous), exist on
the skin and the following tables summarize the most commonly observed, which account for approximately 75% of all skin
tumors. Approximately 20-40% of primary skin tumors are malignant in dogs and 50-65% are malignant in cats.
Occasionally, the observed skin tumors are not primary tumors but rather metastasis from other organs. This is especially
important in cats in which lung cancer commonly metastasizes to the skin.

Percentage of top 10 nonlymphoid skin tumors in dogs (based on 6,282 cases)

Source: Withrow Stephen J, and David M. Vail. Small Animal Clinical Oncology. St Louis: Saunders Elsevier, 2007.

Percentage of top five skin tumors in cats (based on 1,155 cases)

Source: Withrow Stephen J, and David M. Vail. Small Animal Clinical Oncology. St Louis: Saunders Elsevier, 2007.

How common are skin tumors in cats and dogs?
Tumors of the skin and subcutaneous tissues (underneath the skin) are the most common tumors affecting dogs,
accounting approximately for one third of all tumors. In the cat, skin and subcutaneous tumors are the second most
common cancer (after lymphoma), accounting approximately for one fourth of all tumors. Estimates for annual incidence
are ~450 per 100,000 for dogs and ~120 per 100,000 for cats. The incidence for non-melanoma skin tumors is estimated
at ~90 per 100,000 for dogs and ~35 per 100,000 for cats.

What are the symptoms of skin tumors in cats and dogs?
Skin tumors are usually discovered by the pet owners as abnormal growths on the skin while examining or grooming the
pets. Benign tumors are more likely to be slow growing over the course of several weeks to years, and most benign tumors
are seen by veterinarians due to self-trauma (eg licking) or secondary inflammation. Most benign tumors are painless, with
well defined boundaries and freely movable whereas malignant tumors tend to be rapidly growing, fixed to underlying
structures, and ulcerated with ill-defined boundaries.

How is the diagnosis made?
Every skin tumor should be first examined for size, location, ulceration and whether it is freely movable or fixed to
underlying. However, in order to determine the exact nature of the mass, either
cytologic or histopathologic analysis of the
mass should be done in order to design an appropriate treatment strategy and predict the pet's prognosis. The commonly
used diagnostic procedures for skin tumors are fine-needle aspiration cytology and
tissue biopsy. Cytology is an important
tool that can help the veterinarian distinguish a tumor from inflammatory lesions and to evaluate whether the present mass
spread to the lymph nodes but only histopatho
logic examination of the tumor can definitively establish the tumor's type,
grade (level of aggressiveness), what treatment is most appropriate and prognosis about future behavior. The biopsy
technique used will largely depend on the tumor's size and location. Small masses are usually completely excised and sent
to the pathology lab to confirm that the surrounding healthy tissues that were excised along with the tumor do not contain
any cancer cells (indicating successful tumor removal). If the tumor is larger, a small sample is removed for analysis and
depending on the results, appropriate treatment is chosen. Depending on the tumor type and its known level of
aggressiveness, additional diagnostic tests can include blood tests to assess the overall health of the pet, chest X-rays to
check for lung metastasis, and abdominal ultrasound to check for metastasis to other internal organs (eg liver, spleen).
Advanced imaging such as CT (computed tomography) or MRI (magnetic resonance imaging) can be very useful in
evaluating the extent of the pet's disease but, unfortunately, are not readily available in every area.

Does cancer cause pain in pets?
Pain is common in pets with cancer, with some tumors causing more pain than others. In addition to pain caused by the
actual tumors, pets will also experience pain associated with cancer treatments such as surgery, radiation therapy or
chemotherapy. Untreated pain decreases the pet's quality of life, and prolongs recovery from the illness, treatment or
injury. It is, therefore, essential that veterinary teams that are taking care of pets with cancer should also play a vital role in
educating pet owners about recognizing and managing pain in their pets. The best way to manage cancer pain in pets is to
prevent it, a term referred to as preemptive pain management. This strategy anticipates pain ahead of time and
administers pain medication before the pet actually experiences pain, thus ensuring the pet's maximum comfort.

To learn more about which tumors are likely to cause a lot of pain, how to recognize pain in pets with cancer and what
cancer pain management options are available for your pet, please visit the
Cancer Pain Management section.

How important is nutritional support for pets with cancer?
Cancer cachexia (a term referring to progressive severe weight loss) is frequently observed in pets with cancer. Pets with
cancer lose weight partly because of lack of appetite and partly because of cancer-induced altered metabolism. Some of
the causes for decreased appetite are related to the cancer itself (for example, tumors may physically interfere with food
chewing, swallowing, and digestion process) and some may be related to the side effects of cancer treatment (for example,
some chemotherapy drugs cause nausea and vomiting, and radiation therapy can cause mouth inflammation).

Proper nutrition while undergoing cancer treatment is essential to maintain your pet's strength, improve survival times,
quality of life and maximize response to therapy. Adequate nutritional support was shown to decrease the duration of
hospitalization, reduce post-surgery complications and enhance the healing process. Additionally, pets with cancer need to
be fed diets specifically designed to provide maximum benefit and nutritional support for the patient. To learn more, please
visit the
Cancer Nutrition section.

What are the treatment options for cats and dogs with skin tumors?
For specific treatment options for the following skin tumor types, please click on the link:
Mast cell tumors (dog)
Mast cell tumors (cat)

General approach to treating skin tumors in cats and dogs:
In many cases, skin tumors are treated before their exact type is even known (eg via excisional biopsy during which the
entire tumor is removed and sent to the lab for analysis). The specific treatment options will depend on the tumor's type,
location, size, anticipated level of aggressiveness and whether the cancer has spread to other organs throughout the pet's
Surgical removal of the tumor remains the standard treatment of choice. The goal of the surgery is to not only
remove the tumor itself, but also some of the surrounding healthy tissues to ensure that all of the cancer cells that might
have escaped to adjacent tissues are taken out during the procedure. If the tumors are very large, surgery is used to
remove as much of it as possible to provide relief to the pet prior to initiating additional forms of therapy such as
therapy, chemotherapy, or immunotherapy. If the large tumors are located on the limbs, amputation of the affected limb
should be considered. For
mast cell tumors and soft tissue sarcomas, surgery followed by radiation offers an attractive
alternative to amputation.

For tumors located in accessible areas, other treatment modalities can be applied such as
cryosurgery, laser ablation,
photodynamic therapy, and/or hyperthermic therapy.

The main advantage of cryosurgery are speed, avoidance of general anesthesia in most cases, and low cost. It is
particularly useful for small, noninvasive, easily accessible tumors (eg on the tip of the nose, ear tips, eyelid, lip, or perianal
area) and/or in older animals when anesthesia is a concern. The major disadvantage of cryosurgery is that it cannot be
assessed whether all of the cancer cells were successfully removed since none of the healthy tissues surrounding the
tumor are removed as they are during surgery.

Radiation therapy can be used alone as a primary treatment for some skin tumors or in combination with surgery. In some
cases, radiation therapy may produce a better cosmetic appearance in the pet compared to surgery.

Chemotherapy (systemic or topical) has been also used for the treatment of skin tumors. It is usually applied in cases
where surgery and/or radiation therapy are not possible or for treatment of highly aggressive tumors to prevent/delay their
spread throughout the body. Unfortunately, not enough studies have been done to establish which drugs and doses
provide the best benefit.

How do I find a qualified veterinary oncologist?
To locate a qualified veterinary oncologist worldwide who can discuss with you appropriate cancer treatment plan for your
pet's cancer condition, please visit the "
Locate a veterinary oncologist" section.  

Are there any clinical trials investigating new treatments for skin tumors in cats and dogs?
There are clinical trials available for dogs with skin mast cell tumors. To learn more about these trials (which are fully
funded by the institutions), please visit
Mast Cell Clinical Trials for Dogs.

There are clinical trials available for dogs with melanoma. To learn more about these trials (which are fully funded by the
institutions), please visit
Melanoma Clinical Trials for Dogs.

There are several clinical trials ongoing for dogs with soft tissue sarcomas, which are partially funded by the institutions. To
learn more about these trials, please visit the
Clinical Trials for Soft Tissue Sarcoma in Dogs section.

There are available clinical trials (which are partially funded by the institutions) investigating new treatments for vaccine-
associated sarcomas in cats in Colorado, Georgia, North Carolina and Wisconsin. To learn more about these clinical trials,
please visit the
Clinical Trials for Vaccine-associated Sarcoma section.

Additionally, there are several clinical trials available for cats and dogs with any tumor type for which your pet may qualify.
To learn more these trials (which are partially or fully funded by the institutions), please visit the
Dog Clinical Trials (any
tumor type) or Cat Clinical Trials (any tumor type) section.  

To learn more about veterinary clinical trials in general, please visit the
Pet Clinical Trials section.

What is the prognosis?
The prognosis of skin tumors largely depends on the tumor's specific type, size, location, and level of aggressiveness.
Please check the specific skin cancer types for more detailed prognostic information.

  • Withrow Stephen J, and David M. Vail. Small Animal Clinical Oncology. St Louis: Saunders Elsevier, 2007.
  • Morrison Wallace B. Cancer in Dogs and Cats: Medical and Surgical Management. Baltimore: Williams&Wilkins, 1998.
Percentage of cases
Mast cell tumor
Hepatoid (perianal sebaceous)
Sebaceous hyperplasia/adenoma
Squamous cell carcinoma
Basal cell tumor
Hemangiopericytoma (nerve sheath tumors)
Percentage of cases
Basal cell tumor
Mast cell tumor
Squamous cell carcinoma
Sebaceous hyperlasia/adenoma
© 2007 Pet Cancer Center. ALL RIGHTS RESERVED.
Last updated  2/21/2017
Comprehensive guide to cancer diagnosis and treatment in cats and dogs
Skin Cancer in Cats and Dogs