Pet InfoRx^®
Dog Masses and Tumors

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).

  

  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. 

• 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.

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.

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.

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.