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 these tumors?
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?
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 histopathoogic 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.
What are the treatment options?
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 body. 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
radiation 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.
Are there any clinical trials investigating new treatments?
There are only a few available clinical trials investigating new treatments for skin tumors in pets. To learn more about
clinical trials open to enrollment in the United States, please visit the Clinical Trials for Dogs and Clinical Trials for Cats
sections. To learn more about veterinary clinical trials in general, please visit the Pet Clinical Trials section.
To help Pet Cancer Center conduct more skin cancer trials across the United States in order to make novel and more
efficacious therapies available to pets, please
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.
Additional online resources about skin cancer in pets:
www.caninecancer.com/skincancer.html
Sources:
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 these tumors?
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?
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 histopathoogic 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.
What are the treatment options?
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 body. 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
radiation 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.
Are there any clinical trials investigating new treatments?
There are only a few available clinical trials investigating new treatments for skin tumors in pets. To learn more about
clinical trials open to enrollment in the United States, please visit the Clinical Trials for Dogs and Clinical Trials for Cats
sections. To learn more about veterinary clinical trials in general, please visit the Pet Clinical Trials section.
To help Pet Cancer Center conduct more skin cancer trials across the United States in order to make novel and more
efficacious therapies available to pets, please
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.
Additional online resources about skin cancer in pets:
www.caninecancer.com/skincancer.html
Sources:
- 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.
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© 2007 Pet Cancer Center. ALL RIGHTS RESERVED.
Last updated 11/23/08
| PET CANCER CENTER Comprehensive guide to cancer diagnosis and treatment in cats and dogs |
Skin cancer
