Skin Cancer in Dogs: Symptoms and Treatment

Skin cancer in dogs refers to abnormal growths of skin cells. Skin tumors can be benign or malignant, and they can vary widely in appearance, location, and severity.

Because many tumors look alike from the outside, any new lump or bump should be evaluated by a veterinarian to determine what it is and whether treatment is needed.

What Is Skin Cancer in Dogs?

Skin cancer in dogs is an abnormal growth of skin cells. While the term cancer has come to be used as a synonym for malignancy, not all skin tumors are malignant. Tumors that are not malignant are called benign.

Malignant tumors can spread to other parts of the body through the bloodstream or lymphatic system. Benign masses do not have harmful effects beyond the tumor itself.

Sun exposure (UV radiation) can increase the risk of skin cancer in many species. Dogs with lighter-colored fur and skin are at higher risk of developing certain types of skin tumors.

Beyond sun exposure, further study is needed to determine what causes skin tumors to form. There is a genetic link with some types of tumors, such as the high prevalence of mast cell tumors in Boxers, Bulldogs, Boston Terriers, and Pugs. Some growths can also be caused by viral infections.

If you find a lump or bump on your dog, let your veterinarian know. There are many possible causes for lumps, and many are benign or easily treatable.

Types of Skin Cancer in Dogs

There are several types of skin tumors in dogs, including benign tumors and malignant skin cancers. They can vary in appearance, location, and the dogs they most commonly affect.

Benign Skin Tumors in Dogs

Lipomas

Lipomas are tumors that generally lie just under the surface of the skin. These masses originate from fat/lipid cells.

Lipomas tend to be soft and squishy (fluctuant) and are generally not attached to any underlying structures. They can be quite small (grape-sized) but can grow to be the size of a watermelon.

Histiocytomas

Histiocytomas are generally found on the limbs of younger dogs, usually those less than 2 years old. They originate from a cell type called a Langerhans cell, which is part of the immune system.

These tumors are often called “button tumors” because they tend to be small, round, raised, hairless pink masses. They are fairly common in larger-breed dogs such as Labrador Retrievers, American Staffordshire Terriers, and Boxers.

A true histiocytoma usually goes away (regresses) on its own after about three months.

Papillomas

Papillomas are wart-like growths that commonly occur around the mouth or eyes of younger dogs or dogs with immature or weaker immune systems.

They are caused by the canine papilloma virus, or CPV1. The virus is transmitted through the pet's environment, usually by food or water bowls. It takes about one to two months for the tumors to appear, and they generally go away in that same period of time.

Sebaceous Adenomas

Sebaceous adenomas are tumors that begin in oil glands in the skin. These masses tend to look like raised, hairless, bumpy growths and are generally smaller—usually the size of a pea or blueberry.

They tend to be more prevalent in older, light-colored dogs, particularly small dogs such as Poodles, Shih Tzus, and Maltese.

Malignant Skin Cancer in Dogs

Mast Cell Tumors

A mast cell is part of the immune system and is also involved in allergic reactions. As part of an allergic response, mast cells release histamine, a common mediator of allergies.

Mast cell tumors (MCTs) can release large amounts of histamine at once, a phenomenon called mass degranulation. This causes swelling, itchiness, irritation, and even life-threatening allergic reactions.

These masses can vary in appearance but are typically raised red lumps that may be ulcerated (have an open sore) and have swelling of the surrounding tissue.

Mast cell tumors are the most common skin tumor in dogs, and the average age of occurrence is around 10 years old.

They are most common in Boxers, Boston Terriers, Bulldogs, Pugs, Staffordshire Terriers, Labradors, Golden Retrievers, Rhodesian Ridgebacks, and Weimaraners.

Squamous Cell Carcinomas

Squamous cell carcinomas (SCC) originate directly from the epidermis, or skin cells. These tumors tend to form in older animals, especially those with lighter skin and/or shorter fur.

They are also common on the nose of pets that spend a large amount of time outside. The appearance of a squamous cell carcinoma can vary widely.

It is also the second most common oral tumor in dogs and can occur on the gums or tongue. On the skin, these masses tend to first appear as red or ulcerated skin. Crusting and erosion can also occur.

Melanomas

Melanomas arise from melanocytes, which are the cells that give skin its color through the pigment melanin.

These tumors are generally pigmented (colored), mostly black or brown, and are found in areas of the dog's body that have less hair, especially around the mouth, feet, and eyes.

Melanomas of the toes (or digits) are prevalent in black dogs and may start as swelling around a toenail. Melanomas are also the most common oral tumor in dogs.

These tumors can grow quickly and have a high tendency to spread.

Fibrosarcomas

Fibrosarcomas develop from the connective tissues of the skin and beneath the skin. They are most commonly found on the legs of middle-aged or older dogs.

They usually appear as a firm lump on or under the skin. There may be multiple small lumps in one place.

Pain and swelling may be associated with these masses, which can bleed, open, and become infected. These tumors can also be found around the mouth and nose.

What Are the Symptoms of Skin Cancer in Dogs?

The most common sign of skin cancer in dogs is a change in the skin, such as a new growth, lump, bump, or sore that refuses to heal.

Because these skin changes are highly visible, lumps may be noticed early.

All new lumps and bumps, regardless of size, color, location, consistency, or fur, should be evaluated by a veterinarian.

What Causes Skin Cancer in Dogs?

The causes of skin cancer in dogs are not fully understood, but sun exposure (UV radiation), genetic links, and viral infections can contribute to certain types of skin tumors.

Skin cancer is, by definition, a mass that grows without normal cell regulation from any of the many cell types that make up your dog's skin.

Further studies are needed to determine why cells begin to replicate without the body's normal restrictions on cell growth. Sun exposure can increase the risk of skin cancer in dogs, especially those with light skin colors.

Additional known causes include genetic links, such as those associated with mast cell tumors, and viral infections, such as those associated with papillomas.

How Is Skin Cancer in Dogs Diagnosed?

Veterinarians may diagnose skin cancer in dogs using a needle biopsy, tissue biopsy, X-rays, or advanced imaging, depending on the mass and whether cancer is suspected.

When Should a Lump Be Checked?

Any lump that visibly grows, irritates your dog, bleeds, changes size or color, is larger than a pea, or has been present for a month or more should be checked by your dog's primary care veterinarian.

Many tumors look alike on the outside, so it's important for your veterinarian to check masses and determine a plan for diagnosis and treatment.

A needle biopsy is generally the first step toward a diagnosis, but other testing may be recommended at the same time or at a future visit. A select group of masses or dogs, such as a young dog with a suspected histiocytoma or papilloma, may be monitored before further testing is done.

Needle Biopsy

A needle biopsy, also called a fine needle aspirate (FNA), is a way of collecting a sample of cells from within a mass for evaluation. A needle is inserted into the mass, and cells are either compressed into the needle as it is inserted or pulled into the needle through a syringe. The collected cells are then placed onto a slide and examined under a microscope.

Most needle biopsies are sent to a laboratory, where a veterinary pathologist evaluates the sample. Because this sample contains only some of the cells from the mass, it may not provide a complete overview of the mass.

Some dogs may require sedation for a needle biopsy depending on the location of the mass and the dog's temperament.

Punch or Tissue Biopsy

In some cases, a larger portion of tissue needs to be evaluated. A section of the mass or the entire mass, if it is about 8 millimeters or less, can be removed and sent to a laboratory for evaluation.

Dogs may need local anesthesia, sedation, or full anesthesia for a biopsy, depending on the dog and the tumor's location.

X-Rays

When a tumor is suspected to be cancerous or malignant, there is a risk that it has spread to other parts of the body. The lungs are a very common place for tumor spread (metastasis), so X-rays are often recommended to monitor for signs of malignant cells spreading.

Advanced Imaging

Advanced imaging may include CT (computerized tomography), MRI (magnetic resonance imaging), or ultrasound.

These tests are often used to determine the extent of a tumor that is deeper than skin level. They may also be used to examine lymph nodes around a mass to determine whether a malignant tumor has spread to those areas.

How Is Skin Cancer in Dogs Treated?

Treatment for skin cancer in dogs depends on the tumor type, stage, and location and may include surgery, chemotherapy, radiation, immunotherapy, or a combination of treatments. Many types of skin tumors are treatable, especially if caught early.

Surgery

For most skin tumors, especially tumors that are small and in easily accessible areas of the body, surgical removal is often the first treatment step. Surgery removes most, if not all, cancer cells from the area.

Surgery can be curative, meaning removal of the mass is the only treatment necessary, such as with small benign masses like sebaceous adenomas. It can also be part of a larger treatment plan, such as with melanomas, where spread (metastasis) is common.

Chemotherapy

Chemotherapy is medication given intravenously (IV) or by mouth. These drugs are toxic to cells that divide rapidly, such as those involved in tumor growth.

Chemotherapy is often used for certain types of cancer that are present in multiple locations in the body or after surgical removal of a mass that is already suspected of spreading.

Radiation

Radiation therapy uses a focused radiation beam to target specific tumors, generally in areas where surgical removal is difficult.

Radiation is often used in combination with surgery or chemotherapy.

Immunotherapy

Immunotherapy is similar to a vaccine. For a select number of cancer types, such as melanomas, an immunotherapy vaccine is available.

The vaccine contains killed parts of a cancerous cell. These cell pieces travel through your pet's system, stimulating the immune system to fight cancerous cells.

Immunotherapy is also generally used in conjunction with one or more of the other treatment types.

Recovery and Management of Skin Cancer in Dogs

Recovery and management of skin cancer in dogs depend on the type of tumor present. Your veterinarian will review any diagnostic findings and discuss your dog's recommended treatment and prognosis. They may also refer you to a veterinary oncologist.

Recovery After Skin Cancer Surgery

After surgery, your dog may feel sore, and your veterinarian will likely prescribe pain medication. Follow all medication directions closely.

Many dogs will need crate rest. Your veterinarian will give you a time frame for when your dog can return to normal activity levels.

Managing Chemotherapy Side Effects

If chemotherapy is part of your dog's treatment plan, it can cause:

• Nausea
• Vomiting
• Diarrhea
• Low energy levels

Your veterinarian may prescribe anti-nausea medications or other supportive therapies while your dog is undergoing chemotherapy.

It is also important to ensure that your dog is getting high-quality food to aid in recovery.

How To Prevent Skin Cancer in Dogs

When possible, limit your dog's exposure to the sun, especially during peak UV hours. Dogs with light colors or short fur may benefit from dog sunscreen.

Monitor Your Dog's Skin

Early intervention is extremely important for many types of skin tumors. Monitor your dog for the formation of lumps and bumps and seek prompt veterinary evaluation of any masses you find.

Any mass, even one that has previously been diagnosed as benign, should be evaluated if you notice:

• A change in size
• A change in shape
• A change in color
• Bleeding

Cancerous or malignant masses can recur in the same area, so watch your dog closely for other masses and report them to your veterinarian.