Skin Growth, Lump, Swelling or Mass in Dogs

Skin growths are lumps of tissue that are within the skin or can be felt under the skin. Dogs can develop small bumps (papules) or larger bumps (nodules) on their skin. These lumps and bumps are fairly common occurrences, especially in the older dog.

Below is an overview of skin tumors and lumps in dogs followed by in-depth information about figuring out about benign vs. malignant tumors as well as the diagnosis and treatment of treating skin tumors.

Very often the word “lump” brings the word “cancer” to mind. However, there are many other causes of lumps. A skin growth or mass may be a malignant or benign tumor, an abscess, a cyst, a hematoma (blood-filled mass) or a reaction by the skin to an allergen (hives). Lumps are often benign accumulations of fat called lipomas. However, all lumps should be evaluated for the possibility of malignancy.

When is a Lump Cause for Concern?

Any new lump or bump should be evaluated right away, especially a lump that is rapidly growing, is warm or painful, is ulcerated or bleeding, is irregular in shape or is well attached to the tissues under the skin. Any of the above signs should prompt you to seek veterinary attention.

Different Types of Skin Tumors and Lumps in Dogs

A skin mass or lump can be within the skin, in the tissues under the skin or attached to the skin and underlying tissues. Thus, any proliferation of cells, pocket of fluid or debris, or swelling of the dog’s tissues can cause a mass. The health impact depends on the severity of the cause of the growth and the success in treatment of the problem.

The most common causes of skin growth are tumors, malignant and benign, bruises, infections and other causes.

Malignant Dog Tumors

Malignant tumors are proliferations of abnormal cancerous cells that endanger the dog by either invading nearby tissues or spreading to other areas of the body (metastasis). There are too many types of skin tumors to list here, but some of the more common ones are:

• Mast cell tumors. These are made up of great numbers of mast cells, a type of cell that is normally found within the skin. These cells normally release substances that are involved in allergic and immune responses. The massive amounts of these substances that can be released from tumors can be very dangerous to the animal. Tumors of this type can invade locally and metastasize.
• Melanomas. These are tumors of the cell type that provides pigment to skin. They may be malignant or benign. Melanomas on the feet or in the mouth are likely to be very aggressive and dangerous. These tumors are usually black in color.
• Fibrosarcomas. These tumors affect the cell type that helps to make up the connective tissue found under the skin. They rarely metastasize but are very destructive locally.
• Squamous cell carcinomas are malignant tumors of skin cells that often occur at areas of unpigmented or lighter colored skin due to damage from the sun. They rarely metastasize but are destructive locally. They may also be non-solar induced.

Benign Dog Tumors

Benign tumors are proliferations of cells that do not invade other tissues or spread to other locations. They are only dangerous when growing in a confined space, like in the head where they may compress the brain. They may need removal if they inhibit any important function or if they become damaged and bleed or become a nuisance. Some common benign tumors are listed below.

• Lipomas are benign tumors of fat cells commonly found under the skin in dogs. These tumors are only a problem when they get very large or when they are in a location that interferes with the animal’s movement.
• Perianal adenomas are found under the tail in the skin next to the anus. They occur most commonly in males that have not been neutered. Your veterinarian will probably recommend neutering at the time the mass is removed to prevent future tumors. Fortunately, the malignant counterpart of this tumor, the perianal adenocarcinoma, is rare.
• An abscess is a collection of inflammatory cells (white blood cells) that have been drawn to an area within or under the skin by the stimulation of an infectious agent (fungus or bacteria).
• A hematoma is a blood filled space that can be found under the skin and is usually caused by trauma or by a defect in the clotting system.
• When a dog has an allergic reaction, specific cells will release chemicals that cause swelling and redness in the skin called hives.
• A cyst is a space within or under the skin that is filled with fluid or cellular debris. Cysts are usually caused by abnormalities of skin glands.

Diagnosing Skin Lumps in Dogs

Diagnosis may include the following:

• A complete medical history and physical exam: Expect to answer questions about how long the growth has been there, what it looked like when it appeared and how it has progressed, how fast it is growing and whether it is hot, swollen or painful. Other tests will be needed to determine what the cause of the lump or swelling may be.
• An aspirate of the mass: The aspirate is placed on a slide, stained and viewed under a microscope. Many masses can be identified in this manner. For example, fat cells are found in lipomas and mast cells are found in mast cells tumors. Pus is aspirated from abscesses and debris or fluid is aspirated from cysts. Some tumors are notoriously hard to get cells from and this test may be non-diagnostic. In addition, some cells are difficult to identify when not seen in their normal orientation.
• An impression smear: In this technique, a glass slide is pressed to a moist lesion and stained for examination under the microscope. This is particularly useful in evaluating open abscesses and other infectious lesions. The slide may show not only the characteristic white blood cells, but also an appreciation for the infectious agent (type of fungal or bacterial agent).
• A biopsy: This procedure is used if the problem cannot be determined by other methods. After suitable sedation or anesthesia a piece of the mass is collected by using a biopsy punch or a surgical blade. The biopsy is sent to a veterinary pathologist to determine what kinds of cells are present. A piece of tissue may also be submitted to culture for infectious agents.

Treating Skin Lumps in Dogs

The treatment will depend on the final diagnosis.

Malignant tumors may be surgically removed, treated with chemotherapy, treated with radiation therapy or a combination may be used. Benign tumors often are not removed unless they become a nuisance. Abscesses are often lanced, cleaned and flushed. Once this is done, antibiotics are much more likely to be successful.

Hematomas are treated by identification and elimination of the underlying cause. Hematomas caused by trauma often heal without treatment. Cysts may be opened, drained and flushed, treated by removal of the entire cyst or left alone if they don’t bother the owner or the dog. Hives or other allergic reactions are treated with anti-inflammatory drugs, such as steroids and antihistamines.