Tumors, Growths, and Cysts in Dogs

Healthy puppy after medical exam
gilaxia / Getty Images

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 persistent, 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 a type of cancer.

growths, tumors, and cysts on dogs illustration
Illustration: The Spruce / Kelly Miller

Signs of Tumors, Growths, and Cysts in Dogs

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

  • An abnormal lump or a bump ranging in size from very small to very large
  • Discolored, itchy or irritated skin over a bump
  • A swollen area (particularly within the body)
  • Enlarged lymph nodes
  • Lameness or swelling affecting a bone

Sebaceous Cysts, Adenomas, and Adenocarcinomas

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 or a benign mass called a sebaceous gland adenoma. 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 determine that it is, indeed, just a sebaceous cyst or an adenoma or adenocarcinoma that may require more treatment.

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

Histiocytomas are red bumps that can appear quickly on your dog's skin and tend to go away on their own over the course of a few months. 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. Unlike other common skin masses, histiocytomas are most frequently diagnosed in younger dogs.

Squamous Cell Carcinoma

Squamous cell carcinoma is a type of tumor that may be caused by sun exposure. This type of cancer can occur on the skin and/or in the mouth. These tumors can 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 easily 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.

  • 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 in many cases they will resolve on their own.
  • An epulis is an oral growth that usually forms on the gum tissue around a tooth. 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 or is bothersome to the dog. The removed tissue may be sent to a veterinary pathologist just to make sure there are no cancer cells present.
  • Oral melanoma can occur in the mouth and may be black in color.
  • Squamous cell carcinoma and fibrosarcoma are other common types of cancer that can develop within the mouth of dogs.

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 radiographs can be done.

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 damage). In rare cases, an apparent lipoma is actually a malignant tumor called liposarcoma. Diagnostic testing can differentiate the two.

Mast Cell Tumors in Dogs

Mast cell tumors may occur as skin bumps or internal tumors. These masses may release histamine when disturbed, which can have a negative effect on your dog's body, including the heart. If your vet suspects a mast cell tumor, your dog may be treated first with diphenhydramine to minimize the histamine release. Once the mass is removed, a 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

Mammary tumors are more common in female dogs, particularly in those that are not spayed but can sometimes occur in spayed females as well. Though some mammary masses may be benign, many are cancerous. Prognosis improves when the masses are diagnosed and surgically removed when they are small.

Internal Masses

Some dogs develop internal masses within the chest or abdomen, especially as seniors. Internal masses may be found due to the symptoms they create (difficulty breathing or vomiting, for example) or during a routine physical examination. Internal masses may be benign or malignant and are usually definitively diagnosed through a combination of radiographs, ultrasound, lab work, and biopsy. Treatment depends on the location and type of tumor.

Canine Lymphoma

Lymphoma is not actually a tumor; it is a cancer of certain cells within the immune system. However, the first sign of lymphoma is often an enlargement of the lymph nodes, which can look and feel like tumors.

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. Chemotherapy is the most common treatment for lymphoma.

Causes of Tumors, Growths, and Cysts

  • Sebaceous cysts, adenomas, and adenocarcinomas
  • Skin tags
  • Histiocytomas
  • Squamous cell carcinoma
  • Malignant melanoma
  • Canine oral growth
  • Lipomas
  • Mast cell tumors
  • Mammary tumors
  • Abdominal masses
  • Canine lymphoma
  • ... and many more including cysts (non-sebaceous), hematomas, infections, inflammatory reactions, and swellings that result from injury.

Diagnostic Process

When a lump has been discovered, your veterinarian will perform a physical examination. If the lump is very new and potentially temporary (like the result of a bug bite or an injection), the veterinarian may recommend a period of observation, but in most cases, they will perform additional diagnostics to determine the type of cells that comprise the mass. This usually means collecting a sample of the material from the mass and analyzing it under a microscope.

A veterinarian typically collects these samples via fine needle aspirate or biopsy. Evaluation of the samples (often performed by a pathologist) can indicate whether the mass is cancerous, and if so, what type of cancer is present.

If your veterinarian diagnosis your dog with cancer, 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 problems
  • 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 and some internal organs.

Some advanced diagnostics and treatments 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 of the mass.

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 for identification.

How to Prevent Tumors, Growths, and Cysts

Many lumps, bumps, and growths cannot be prevented, but some can. For example, spaying your dog before her first heat cycle virtually eliminates the chances that she will develop mammary tumors.

In all cases, maintain a healthy diet and an active lifestyle for your dog and see your veterinarian at least annually for preventative care. 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.