Skip to main content


By T. J. Dunn, Jr., DVM

There are very few surprises that will worry you more than discovering a new lump or bump on your dog. As your hand wanders over your canine pal, your fingers just may chance upon a lump that “was not there before." Your first though will probably be along the lines of “What is this?” followed quickly by “I hope it’s not serious.” Read on to learn how abnormal growths in dogs are diagnosed and treated and just how worried you should be.  

Common Lumps and Bumps on Dogs

The question most owners have when they find a new lump or bump on their dog is, "Is it a tumor?". The truth of the matter is that no one can tell you with 100 percent certainty what a mass is by simply looking at it. Your veterinarian may be able to make an educated guess with just an exam, but without taking a sample of cells and looking at them under the microscope or sending them to a pathologist for identification, a definitive diagnosis is simply not possible.

Sebaceous Cysts on Dogs

That said, not every lump or bump on your dog requires a full work-up. Some superficial bumps are just sebaceous cysts, which are plugged oil glands in the skin that are usually nothing to worry about. Other types of skin cysts can be composed of dead cells or even sweat or clear fluid; these often rupture on their own, heal, and are never seen again. Others become chronically irritated or infected, and should be removed and then checked by a pathologist just to be sure of what they are.

Certain breeds, especially the Cocker Spaniel, are prone to sebaceous cysts, and some individuals can develop dozens at a time. Scientists have not yet identified a reason behind the formation of sebaceous cysts in dogs, so at this point veterinarians don’t have much to offer when it comes to prevention. If oily skin or blocked pores are thought to be playing a role, regular baths with a dog shampoo containing benzoyl peroxide may be helpful.

And yes, the sebaceous glands in the skin do occasionally develop into tumors called sebaceous adenomas. According to Dr. Richard Dubielzig of the University of Wisconsin, School of Veterinary Medicine, "Probably the most commonly biopsied lump from dog skin is a sebaceous adenoma. This does not mean it is the most commonly occurring growth, just that it is most commonly biopsied." Fortunately, this type of skin growth rarely presents trouble after being surgically removed. 

Lipomas on Dogs

The lipoma is another commonly encountered lump seen by veterinarians during a physical exam. These soft, rounded, non-painful masses that usually present just under the skin are generally benign. That is, they stay in one place, do not invade surrounding tissues, and do no metastasize to other areas of the body. They grow to a certain size and then just sit there and behave themselves.

How Do I Know Which Lumps are Dangerous

So how are you to know which of the lumps and bumps found on a dog are dangerous and which can be left alone? Truthfully, you are really only guessing without getting your veterinarian involved. Most veterinarians take a conservative approach to masses like lipomas and sebaceous cysts and only recommend removal if they are growing rapidly or causing problems for the dog.

However, every lump that is not removed should be closely observed. Sometimes, those that appear to be benign can turn out to be a more serious problem. Any mass that is growing rapidly or otherwise changing should be reevaluated. 


Types of Lumps and Bumps

Lumps and bumps on a dog's skin can have many underlying causes, which owners often divide into two categories: cancer and everything else.

Non-cancerous lumps

Non-cancerous lumps commonly found on dogs include cysts, warts, infected hair follicles, and hematomas (blood blisters). While generally less worrisome to owners, non-cancerous lumps can still create discomfort for dogs. Your veterinarian can tell you which can simply be monitored and which should be treated.

Cancerous lumps

Cancerous growths on dogs can be either malignant or benign, and occasionally even share characteristics of both. Malignant lumps tend to spread rapidly and can metastasize to other areas of the body. Benign growths tend to stay in the place of origin and do not metastasize; however, they can grow to huge proportions (see such an example of an inoperable tumor pictured on the right).

Mammary gland tumors, mast cell tumors, cutaneous lymphosarcoma, malignant melanoma, fibrosarcoma, and many other types of cancers are commonly diagnosed in dogs.


The most common methods of diagnosing lumps and bumps in dogs are listed below. 

Impression Smears

Some ulcerated masses lend themselves to easy cell collection and identification by having a glass microscope slide pressed against the raw surface of the mass. The collected cells are dried and sent to a pathologist for staining and diagnosis. Sometimes the attending veterinarian will be able to make a diagnosis via the smear; but if not, a specialist in veterinary pathology will have the final say.

Needle Biopsy

Many lumps can be analyzed via a needle biopsy rather than by tissue biopsy. A needle biopsy is performed by inserting a sterile needle into the lump, pulling back on the plunger, and "vacuuming" in cells from the lump. The collected cells are smeared onto a glass slide for pathological examination. Usually the patient isn’t even aware of the procedure. 

Tissue Biopsy

Sometimes microscopically examining a larger chunk of tissue is necessary to reach a diagnosis. The mass may be totally removed or just a small piece taken out (biopsied) to give the veterinarian all the information he or she needs to make a plan for treatment.

CT Scans or MRIs

Diagnosing superficial lumps and bumps typically does not require a CT scan or MRI, so these procedures are usually reserved for internal organ analysis. If a superficial malignant tumor is diagnosed, however, a CT scan or MRI can be helpful in determining if metastasis to deeper areas of the body has occurred.

Radiography and Ultrasonography

As with CT scans and MRIs, X-ray and ultrasound evaluations are generally reserved for collecting evidence of internal masses or metastases.



Since every type of cell in the body potentially could become cancerous, the varieties of tumors that can develop in dogs are numerous. Each case needs to be evaluated based on its own circumstances, but treatment recommendations for lumps and bumps typically include one or more of the following. 


An important basic tool for eliminating a nuisance or dangerous lump is to surgically excise it.


Medications that are highly toxic to rapidly dividing cells are an important mode of treatment for cancers that are present in multiple locations within the body. Chemotherapy is often employed as an additional procedure after a mass has been removed via surgery but has a high likelihood of having metastasized.


For invasive tumors that do not have well-defined borders or are in a location that makes surgery difficult, radiation therapy can be an excellent option. Radiation therapy is available at most veterinary medical schools and some veterinary specialists in radiology. Radiation therapy may be employed in combination with other treatments.


Emerging techniques such as gene therapy and immunotherapy hold promise for offering new ways to combat some types of tumors in dogs. Your veterinarian may be able to put you in touch with veterinary scientists who are looking for patients to enroll in clinical trials.

According to Dr. Dubielzig, the best approach to treating lumps or bumps in dogs is to be observant and treat each situation individually. "In cases where vigilance for tumors is part of the animal’s care, such as in animals where a malignant tumor has been removed and the veterinarian wishes to keep abreast of the stage of disease, then every lump should be submitted for histopathology," Dubielzig said. "In other cases where the clinician is sure of a benign diagnosis such as lipoma or a wart-like skin mass, then it might be understandable to use discretion."

Take a good surface inventory of your dog today, and at least once a month from now on. If you find any lumps or bumps, take heart in knowing that modern veterinary medicine has some very effective remedies for many of the masses that are commonly diagnosed in dogs.

Help us make PetMD better

Was this article helpful?