Tumors, Growths, and Cysts in Dogs

Healthy puppy after medical exam
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It's not unusual to find lumps and bumps on dogs. Growths and masses can appear on dogs at any age, but they are among the most common health issues seen in older dogs. As a dog owner, it's helpful to understand the different types of growths you may encounter. Any unusual mass or growth should prompt a call to your veterinarian.

What Are Tumors, Growths, and Cysts?

Most veterinarians will call any unknown lump or bump a growth, mass, or a tumor. In general, the terms can be used interchangeably, but most vets avoid the word tumor unless the mass has been determined to be malignant.

illustration of growths, tumors, and cysts on dogs
Illustration: Kelly Leigh Miller. © The Spruce, 2018

Signs of Tumors, Growths, and Cysts in Dogs

Abnormal growths can occur anywhere on the body or in the mouth. Warning signs include:

  • A lump or a bump ranging in size from very small to large
  • A red, itchy bump
  • A swollen area (particularly within the body)
  • Enlarged lymph nodes
  • Lameness or swelling in the bone

Sebaceous Cysts

Sebaceous cysts are common types of skin cysts that contain sebum, a thick, oily material normally found in the skin around the hair follicles. These masses may be found anywhere on the body. Sebaceous cysts are benign but can also be mistaken for a malignant tumor called a sebaceous gland adenocarcinoma. If the cyst does not bother your dog, your vet might leave it alone, but a cyst can be surgically removed if necessary. Once removed, the cyst should be sent to a lab so a veterinary pathologist can analyze it just in case there are some malignant cells present. 

Skin Tags

Skin tags on dogs are similar to those humans get. Some can get quite large and pendulous, hanging off the skin by a narrow stalk. Skin tags are benign and are usually not removed unless they bother the dog or get very large and irritated. 


Histiocytomas are red bumps that can appear quickly on your dog's skin. Although they are benign tumors, some can grow rapidly and really bother your dog. Your vet may recommend the removal of large or irritated histiocytomas.

Squamous Cell Carcinoma

Squamous cell carcinoma is a type of tumor that may be caused by sun exposure. This type of cancer can also occur on the skin and/or in the mouth. These tumors often have a pink or reddish color and misshapen, "raw" appearance.

Malignant Melanoma

Malignant melanoma can occur on the skin and/or in the mouth and is thought to be caused by sun exposure. Many of these tumors have a black color but not all will look the same.

Canine Oral Growths

There are many kinds of growths that can develop in your dog's mouth. Some growths cannot be seen but will cause signs like bad breath, trouble chewing, difficulty holding things in the mouth, oral pain, and pawing at the face or mouth. Of course, these signs could also indicate dental disease and should not be ignored.

  • Oral papillomas are warts caused by the papillomavirus. They can appear on the dog's lips, face, and inside the mouth. Papillomas are benign but very contagious. They can be removed if they cause problems for your dog, but they will eventually come back.
  • An epulis is an oral growth that usually forms on the gum tissue. Many epulides are benign, but some can be malignant, so further diagnostics are necessary.
  • Gingival hyperplasia is a benign overgrowth of gum tissue that may look a little bit like a tumor in some dogs. This excess gum tissue can be removed if it's affecting the teeth. The removed tissue may be sent to a veterinary pathologist just to make sure there are no cancer cells.
  • Oral melanoma can occur in the mouth and may be black in color.

Some oral tumors can affect the teeth and bone in the mouth and face. If your dog has an oral mass, your vet will likely recommend putting your dog under anesthesia so a thorough examination and dental radiographs can be done. If there is dental tartar or gum disease present, your vet is also likely to recommend a professional dental cleaning while your dog is under anesthesia.

Lipomas in Dogs

Lipomas are among the most common types of tumors seen in dogs. A lipoma is a benign fatty mass that can be found anywhere on a dog's body, typically under the skin. They usually feel soft and moveable and rarely cause pain or discomfort for the dog. Lipomas can be surgically removed if they interfere with your dog's mobility or comfort, grow rapidly, or rupture (causing skin irritation). In rare cases, an apparent lipoma is actually a malignant tumor called liposarcoma.

Mast Cell Tumors in Dogs

Mast cell tumors may appear as small skin bumps or internal tumors. These are often malignant tumors that release histamine when disturbed with tests like a biopsy or FNA. This excess histamine release can have a negative effect on your dog's body, including the heart. If your vet suspects a mast cell tumor, your dog will be treated first with diphenhydramine to minimize the histamine release. The pathologist will grade the tumor as I, II, or II. This grading indicates how malignant the tumor is and how likely it is to metastasize (spread to other parts of your dog's body).

Mammary Tumors in Dogs

In female dogs, any inflammation of the mammary gland should be addressed as soon as possible. Inflammation of the mammary gland is called mastitis. However, the inflammation may be caused by a tumor. Though some mammary masses may be benign, many are cancerous. Mammary cancer is more common in intact females (not spayed) but can sometimes occur in spayed females.

Abdominal Masses

Some dogs develop abdominal masses, especially as seniors. Abdominal masses are usually found when your dog's abdomen is palpated on examination or when routine abdominal radiographs are performed. Treatment depends on the location and type of tumor.

Many abdominal masses are malignant and most are attached to an organ. If your vet finds or suspects an abdominal tumor, often the first step is to do abdominal radiographs and/or abdominal ultrasound. Chest radiographs are done to check for metastasis in the lungs. Your vet might recommend referral to a veterinary specialist for advanced diagnostics and expert recommendations. Some abdominal tumors can be biopsied to determine malignancy. They are usually surgically removed if this is possible.

Canine Lymphoma

Lymphoma is not actually a tumor; it is a cancer of the lymphatic system. However, the first sign of lymphoma is usually an enlargement of the lymph nodes. This inflammation may look like tumors to you because the lymph nodes become very large, round, and lumpy.

Pet owners most often notice lumps in the neck area, but they may also be found in the axillary area (armpits), the inguinal area (lower abdomen near thighs), and the back of the knees. Lymphoma is often diagnosed with a fine needle aspiration or biopsy, but the lymph nodes are not typically removed. Chemotherapy is the most common treatment for lymphoma.

Causes of Tumors, Growths, and Cysts

  • Sebaceous cysts
  • Skin tags
  • Histiocytomas
  • Squamous cell carcinoma
  • Malignant melanoma
  • Canine oral growth
  • Lipomas
  • Mast cell tumors
  • Mammary tumors
  • Abdominal masses
  • Canine lymphoma

Diagnostic Process

When a lump has been discovered, your veterinarian will perform a physical examination. In most cases, your vet will recommend additional diagnostics to determine the type of cells that comprise the mass. This usually means collecting a sample of the material inside the mass and analyzing it under a microscope.

A veterinarian typically collects these samples via fine needle aspirate or biopsy. This test can indicate whether the mass is malignant or benign. If malignant (cancerous) it can determine the type of cancer present.

If your veterinarian finds a tumor, additional diagnostics will most likely be recommended, including:

  • Lab tests such as blood chemistry, complete blood count, and urinalysis
  • Radiographs (X-rays) that can reveal signs of metastasis or other internal abnormalities
  • Ultrasound, which can offer a better view of internal organs and look for metastasis
  • CT scan or MRI, which will help vets get a closer look at the structure of your dog's tumor (if internal) and the internal organs.

Some advanced diagnostics must be performed by a veterinary specialist.

When Your Dog Needs a Biopsy

If a fine needle aspirate is not effective (or if your vet thinks it's not the best option) the next recommendation is usually a biopsy. A biopsy is often performed with the dog under general anesthesia or sedation, but local anesthesia may be used instead depending on the size and location.

The biopsy may be performed by using a special large needle. Or, the vet may cut into the mass surgically. In some cases, the entire mass is removed surgically and sent to a laboratory.

How to Prevent Tumors, Growths, and Cysts

Most lumps, bumps, and growths cannot be prevented. Maintain a healthy diet and an active lifestyle for your dog. Adhere to a regular grooming schedule and take note of any lumps or bumps that are new. A photo and a written record can help track growth and if you see rapid change, speak to a vet right away.

If you suspect your pet is sick, call your vet immediately. For health-related questions, always consult your veterinarian, as they have examined your pet, know the pet's health history, and can make the best recommendations for your pet.