Signs and Treatment for
Skin Cancer in Dog Problems

Many owners are surprised to learn that skin cancer in dog problems are fairly common. Labradors in particular have a genetic issue that lead to an increased risk of mast cell tumors, soft-tissue sarcomas and dog skin melanomas.

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Dogs can get a wide variety of cancers, including lumps under the skin. It is uncommon for dogs to get cancer from the sun since most areas are covered with hair.

The first sign of dog skin cancer is when they feel a lump on or under the skin when grooming. A dog might chew the area, and there might be a smell in the area or some type of discharge. The only way to determine what caused the lump is for a Vet to examine a sample with a fine needle under the microscope.  This will enable the Vet to determine the cause and the risk to the dog.

The most common type of canine cancer are mast cell tumors. Most are benign, which means slow growing or spreading. Malignant dog tumors refers to neoplasms or tumors that are dangerous due to their risk of spreading. Mast cell tumors can be found anywhere in a dogs body. 

How to Detect Skin Cancer in Dogs

Canine Mast Cell Tumors

Canine mast cell tumors account for up to 20% of all skin cancer in dog cases diagnosed. The mast cell tumors, named after cells that have the pigment melanin, occur in the skin, mouth (dog oral melanoma) and under the dog's toe nails (called canine ungual melanoma). The disease can also occur in the dog's eyes (called ocular or uveal melanoma). The disease varies in severity based on where it is located.  Canine oral melanomas spread faster than other types of melanomas.

Labrador Retrievers have an increase risk of getting oral melanomas when compared to other dog breeds.

Magnified Granulated mast cells from a dog skin cancer tumor caused by a mast cells
Source: Washington State University

What are Canine Mast Cells?

Canine mast cells are found in the tissues of the body. They are an integral component of the immune system. The cells contain proteolytic enzymes (breaks down the cell components protein, heparin and histamine).

Which dogs are at risk for developing mast cell tumors?

Mast cells are found in dogs of any age, but older dogs (age 8.5 - 9.5) are at higher risk. In Labradors there is a genetic factor that leads to a higher tumor incidence.  Other breeds at risk include breeds with short wide heads (brachiocephalic breeds) such as Bulldogs, Pugs, Boston Terriers and Boxers. Golder Retrievers also are at higher risk.

Researchers are not sure what causes the disease. Some suspect that a virus triggers the illness.

What are mast cell tumor symptoms?

Mast cell tumors vary in appearance. They can be malignant (cancerous, fast growing and spreading) or benign (no cancerous). They are more commonly found on the dog's genital area, limbs and trunk. They can be located under the skin or on the skin surface. The tumor itself might be ulcerated, bumpy or smooth.

Other symptoms associated with canine mast cell tumors include:

• blood in the stool
• problems with blood clotting
• duodenal ulcers (small intestine ulcers)
  
• vomiting
  

How are mast cell tumors diagnosed?

Because of the numerous ways it can appear on the skin, a veterinarian will take a sample for analysis using a needle aspirate (collecting cells through a needle).

Mast cell tumors are commonly graded and staged, meaning classified as to how they are expected to behave. This is performed by examining the tumor after it has been removed. The grading and staging help determine what type of further treatment may be necessary and the prognosis.

Grading Canine Mast Cell Tumors

Once the tumor is diagnosed ,a veterinarian will "grade" the tumor in order to classify how ti should be treated. Higher numbers or grades are associated with more serious cases of the disease.

• Grade 1: These tumors are not cancerous (benign) and not considered dangerous. Benign tumors are slow growing and usually do not spread. Most tumor diagnosis are Grade 1.
• Grade 2: These tumors extend from the surface into the lower subcutaneous tissue. The tumors are partly malignant and when treated do not always lead to a predictable result. 
• Grade 3: Tumors that are grade 3 extend deep into the skin and are the most chronic form of tumor.
  

Staging Mast Cell Tumors in Dogs

A veterinarian will also stage the tumor to indicate how quickly it will spread. Staging is done after the surgeon has removed the tumor and inspect adjacent lymph nodes. Staging varies based on how many tumors are found and if the cancer has spread to nearby lymph nodes.

• Stage 0: When only one tumor is found and it is removed. Lymph nodes are not involves.
• Stage 2: The tumor is in the skin and spread to nearby lymph nodes.
• Stage 3: Several lymph nodes are discovered, the tumors are deep into the skin, and there may or may not be spreading to the lymph nodes
• Stage 4: Multiple tumors are found that are spreading, including to the lymph nodes. This stage is further divided into tumors that have so other signs (a) and those that are causing other clinical problems (b)
  

How are mast cell tumors treated?

There are several canine mast cell tumor therapies available. Which ones are used varies based on the specific diagnosis reached by the veterinarian.

Canine Tumor Surgery

Surgical removal is the leading approach to any dog mast cell tumor. It will be a cure for most Grade 1 and Grade 2 tumors. The surgeon will remove the tumor and the area directly around the tumor to make sure that all cancerous cells are eliminated. This is called the margin.

Canine Tumor Radiation

Where the tumor cannot be removed or in more advanced cases, a dog might require the use of radiation. In general, the use of radiation after surgery has lowered tumor re-occurence and has improved the survival rate. It is particularly effective in treating tumors that have not spread to other parts of the body.

Skin Cancer in Dog Chemotherapy

Once a tumor spreads, then treatment needs to take into consideration the need for reaching many parts of the body. Cancer medications work in this way. Agents such as lomustine, vinblastine, prednisone and corticosteroids are all used in conjunction with surgery and radiation. The downside is that dogs do not respond well to chemotherapy.

What is the prognosis for dogs with mast cell tumors?

The mast cell cancer prognosis is dependent on the stage and grade determined by the Vet. Low grade tumors have a better prognosis. The same goes for staging, with lower stages having a better prognosis than higher stages.

Dogs that have mast cell tumors on the legs have the best prognosis. Canine tumors found on the mouth, muzzle, genitals and nail bed have a poorer prognosis. Tumors found on the bone marrow, spleen and other internal organs have a prognosis that isn't as good as other areas of the body.

The Bottom Line on Canine Mast Cell Tumors

There are of a number of ways a mast cell tumor can appear in the body, and multiple symptoms and prognosis. A veterinarian cannot diagnose the condition by just looking at the tumor. They need to take a biopsy or tissue sample and examine it under the microscope for a specific and final diagnosis.

To treat the problem, a veterinarian will look to surgery first, followed by radiation and chemotherapy. If you suspect a skin cancer in dog problem, be sure to bring it to your veterinarian's attention as quickly as possible. Early treatment is easier than treating a mast cell tumor that has spread.

References Skin Cancer in Dog

Mast Cell Tumors in Dogs

Skin Cancer in Dog Related Articles

Lymphoma In Labradors 

Skin Cancer In Dog Care And Treatment 

Breast Cancer In A Dog 

Dog Bone Cancer 

Labrador Retriever Health - An Overview

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