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Dog Masses and Tumors

You have found some masses or lumps on your dog. Before you panic, you need to consult with your veterinarian.

This information prescription explains some general terms used when talking about masses or lumps and describes the most commonly found ones on dogs and what to do after a diagnosis.


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Did You Know?

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Dogs get cancer at about the same rate as humans. But cats tend to get fewer cancers. Between 20% to 40% of the tumors found on the skin are malignant (cancerous). Often they can be cured by surgical removal as long as there has been no spread (metastasis).

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What Is a Mass or Tumor? What Is Neoplasia?

When discussing masses or tumors with your veterinarian, it is helpful to understand what each term means so that communication is clear and understandable.

Mass or Tumor: Generally, when the term mass, tumor, or lumps or bumps are used, it is often describing the actual physical appearance or swelling under the skin. Sometimes it's in reference to a change in skin color or texture, like a mole-like marking. 

Neoplasia: This term generally instills fear in people’s minds because they automatically think of cancer. So, let’s clear up a few more things. Neoplasia simply means that there is an uncontrolled and abnormal growth of cells or tissue. A neoplasm (the tumor) can be benign or malignant.

Benign neoplasia: These tumors are not cancerous or harmful. It tends to grow slowly and does not spread throughout the body.

Malignant neoplasia: These tumors are cancerous and can cause harm. They tend to be unpredictable and can spread to other parts of the body. When they spread on the body, they can invade and destroy those tissues they spread to. This is referred to as metastasis.

Metastasis: This is the spread of the tumor to other parts of the skin but also to organs such as the lungs, liver, etc. This process is not good and leads to disease.

Read the next section below for the description of different masses and how they happen.

The Most Common Masses and Tumors. How Do They Happen?

These are the more common benign and malignant masses that are generally found on dogs. Remember benign masses or lumps are generally harmless.

The only way for a veterinarian to know if the mass is benign or malignant is to take a sample of the mass. This can be done a few different ways. First it can be done by a fine-needle aspirate, where your veterinarian inserts a needle into the mass and draws off cells for analysis. Second, your vet can surgically remove a small section of the mass and send it to a lab for analysis. Lastly, your vet can remove the whole mass and send it to a lab to be analyzed. The lab determines if the cells are benign or malignant.

Common benign lumps you may find on your dog:

    • Papilloma (warts): They appear on the body and can also appear in the mouth (oral wart).
      papilloma wart dog skin issue
      Example of a Wart
      Those dogs who are affected are usually younger than 2 years old for the oral form. There is no set age for those warts that appear along the body. They are typically small, and most often, there are several of them. They are caused by a virus. All pets can carry viruses, but not all show the signs. When a dog's immune system is compromised, then the virus's side effects are often seen. Some things that compromise a dog’s immune system are age (young puppies or senior dogs), long-term steroid treatments, illness, etc. They can disappear spontaneously, but there are times they can become inflamed and infected, which then requires treatment. There are occasions when they are surgically removed (for example, because the dog keeps scratching at them).

    • Sebaceous cyst: Normally, these cysts affect young adult to middle-aged dogs. The lumps can appear almost anywhere on the body. They will generally be small and firm but can get to about an inch in size. Basically, it occurs when an oil gland in the skin gets clogged – think of a pimple! Just like a pimple, they can rupture or pop. When they do rupture or pop pus and/or blood, your dog will likely need it treated by your veterinarian. Periodically, they have to be surgically removed, but it is a minor procedure. 

    • Histiocytoma: Of those dogs affected, 50% are less than 2 years of age. These masses are small, firm, raised, fur-less lumps that can appear almost anywhere on the body. But some common locations include the head, ear flap, and limbs. They are usually non-painful, solitary, and fast-growing. They can spontaneously disappear on their own within 3 months. Surgery is not generally needed but gets rid of them if done. 
histiocytoma dog skin mass
Example of Histiocytoma
  • Lipomas: A very common tumor comprised of fat in dogs. These tumors are normally seen in middle-aged dogs. Female dogs tend to develop them more frequently than male dogs. They usually develop just under the skin. But they can grow between layers of muscle. They can be small or large, singular or multiple, and typically are semi-soft to firm. The rate of growth can vary from very slow to fairly quickly. The rate of growth and location determines if and when surgical removal is needed. While the exact cause of lipomas is poorly understood, it has been determined that high-fat diets can cause considerable growth if the tumors are already present.
lipoma dog skin mass
Example of Lipoma

Common malignant lumps you may find on your dog:

  • Mast Cell Tumors: This tumor represents 20 to 25% of all skin tumors in dogs. The average age for dogs to get them is 8 years old. They arise from mast cells, which is a type of cell that exists in tissue. For dogs, they are extremely variable in shape or size and can resemble other skin tumors as well as be in the center of lipomas. Generally, they are solitary, but there can be several of them. They are usually located on the trunk (the main part of the body) and perineum (the area around the anus) 50% of the time, the extremities (limbs) 40% of the time, and only about 10% of the time are they on the neck and head. Mast cell tumors require removal with large margins around them because the tumor can branch out. Think of an octopus – the head is the main tumor, and the legs are the branches or extensions of it.

  • Malignant Melanoma: This is a type of tumor, like humans, that affects melanocytes in the skin (the pigmented cells of the skin). There is also a benign form of this tumor call melanocytoma. They occur in dogs that are 10 years or older. While they can appear anywhere on the body, their tendency to be benign versus malignant seems to be determined by where they are located on the body. Of those identified, 80% will be in the oral cavity (tongue, lips, gingiva, hard and soft palate, which is the roof of the mouth). These typically are black singular tumors that aggressively invade the surrounding tissue and bone. One must note, however, not all will appear ‘mass-like.’ Some can be a mix of pigments, pink and black, and be more like a flat lesion. Malignant melanomas will appear at the nailbeds, where the nail meets the paw, about 15 to 20% of the time. Again, like the oral form, these are aggressive tumors. Dermal melanomas are dark pigmented, either singular or multiple masses in the haired sections of skin, with 85–90% being benign. These will rarely invade surrounding tissue. 

  • Cutaneous Lymphoma: The different forms of lymphoma (in the lymph nodes), gastrointestinal, etc., represent about 7 to 14% of all cancers seen in dogs. Of the several forms of lymphoma, the cutaneous form (on the skin) is one of the common ones. It can present in a variety of ways. At first, it can appear as flaky, dry, itchy, red patches of skin anywhere on the body. Its presentation variety can often cause it to be mistaken for other skin issues such as allergic dermatitis. As it progresses, the skin becomes thickened and ulcerated. The typical locations that it appears are around the lips, the eyelids, the skin around the penis, and around the back end in the area of the anus/rectum and vulva.

The cause of most benign and malignant masses is generally poorly understood. There is believed to be some genetic and breed predispositions as well as a thought that environmental toxins and diet may play a part. But generally, the causes usually involve many factors.

What You Should Do If Your Dog Has a Lump or Mass

dog mass removed from headThe moment you notice a mass, lump, or bump on your pet, make an appointment with your veterinarian. The sooner the issue is addressed, the sooner you will have peace of mind and the appropriate treatment can be started, which could be a "wait and see" approach, surgery, chemotherapy, etc.

Some masses, such as papillomas (warts), sebaceous cysts, and histiocytomas, may spontaneously improve on their own. This requires patience of about 3 to 6 months. Just be sure that there are no changes to the mass. If there are, call your veterinarian for advice. It helps to take photos of the mass every couple of weeks to judge how it is changing and how rapidly. These photos can be sent to your veterinarian for evaluation too. They'll then let you know if your dog needs to come in for an exam and treatment.

*NOTE* Always resist the temptation to "pop” a sebaceous cyst. Not only can you cause an infection, but you can also cause your pet a lot of pain.

Some tumors may require surgical removal, especially if your dog constantly bites, licks, or chews at it or if it continuously bleeds.

The inset photo above is an example of a benign mass that was surgically removed. Read more on how to care for your dog after surgery.


How Do You Know Things Are Improving?

How things improve depends on the type of mass that your dog has.

If a benign neoplasia happens to get infected and your veterinarian prescribes medication, you will see the redness improve, the mass may get smaller (but may not), and your pet will seem more comfortable.

If your dog had their mass removed surgically, the surgical site will decrease in redness and bruising. Your dog will continue to seem more comfortable and show fewer signs of pain.

dog after surgery wearing a cone

How Do You Know When Things Are Not Improving? What You Should Do.

If the mass or lump continues to grow, changes appearance (gets red, ulcerated, bleeds, etc.), or your pet will not leave it alone, you need to contact your veterinarian.

If your pet had the mass surgically removed and you notice that the incision site is red, hot to the touch, continued bruising or staples/sutures are missing, you need to contact your veterinarian.

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How to Prevent This from Happening in the Future

More often than not, you can’t prevent most masses, lumps, or bumps.

With sebaceous cysts, because they are caused by oily skin, some shampoos can help. Ask your veterinarian for some of their recommendations. By removing the excess oil from the skin, the glands tend to get blocked less often.

Always feed your dog a proper well-balanced diet so that your pet can maintain a good nutritional status. Avoid high-fat foods. It's also recommended to provide your dog with fish oil. Not that it will prevent masses or tumors, but it is a natural anti-inflammatory and has positive effects on the skin.

One important thing you can do weekly is a whole-body check of your pet by looking AND feeling for masses, lumps, bumps, or anything that doesn’t seem normal. If you regularly look over and feel your pet’s body, you will begin to know what is normal, and anything abnormal will be obvious quickly. The sooner you address any issues, the sooner diagnosis and treatment can be started.

If your dog is groomed by a professional regularly, they will hopefully alert you to anything abnormal, but it's still important to keep tabs on your dog's skin. Between you, your vet, and your groomer, you should be able to catch any abnormalities early.

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