It’s A Lump!!!

Client: My Fluffy has a lump on their leg. Doc, is it cancer? What do I need to do? Is he going to die?!?!?! It JUST showed up last night!!! How much is it going to cost???

Veterinarian: Take a deep breath and let’s evaluate this.

The conversation above happens multiple times a day in veterinary offices throughout the world. 

New lumps, bumps, or masses can be found on our pets at any age. New masses can turn out to be a variety of things:

  • Abscess or infection under the skin
  • Inflammation
  • Cysts
  • Cancer

But wait, Dr. Michelle, those are not many options, and you have the scary word CANCER! Yes, you are correct on that observation. I need to make sure I clarify terminology. 

Cancer is defined by Oxford Language as “a disease caused by an uncontrolled division of abnormal cells in a part of the body.”

The critical information and terminology veterinarians and owners need are whether a cancerous mass is benign or malignant.  

Benign – A benign tumor or growth will not invade nearby tissue or spread to other parts of the body. Examples of benign tumors in dogs include lipomas, basal cell tumors, histiocytoma, and ceruminous gland adenoma.

Malignant – Malignant growths invade and kill nearby tissue and spread to other parts of the body, including lungs, spleen, and liver. Examples of malignant growths in dogs include mast cell tumors, carcinomas, or sarcomas.  

Assessment of a Lump, Bump, Mass

Superb Doc, thanks for the English lesson! Now, what do we do? (Typically, this is said sarcastically and exasperated by a client because I like to talk a lot!)

The next step is to assess the 1-2-3 rule used by the oncologist for lumps.

  1. Has the mass been present for more than a month?
  2. Has it doubled in size since you first noticed it?
  3. Is it greater than 3 cm (approximately 1 inch) in diameter?

If the answer is yes to ANY of these questions, additional evaluation of the mass needs to happen.  

Step 1: What is this growth?

Schedule an appointment with your veterinarian for assessment of the mass. Before your appointment, please be prepared for the following questions:

  1. Where is the mass?  

You may think this is an easy question to answer, but you would be wrong!! So many appointments I have spent searching for 5 to 10 minutes trying to find the mass. If you send your significant other, child, caregiver, or random stranger off the street in with your pet for the appointment, make sure they know where the lump is.  

Ways you can help your veterinarian with this question include shaving the area, circle with a permanent marker, or mark on a diagram of a dog or cat.

  1. How long have you known the mass has been present?
  2. Has the mass grown since you first noticed it?
  3. Has the mass changed shape or texture?
  4. Does your pet have a history of other growths or cancer?

Once the veterinary staff has obtained this information, your veterinarian will examine your pet. 

During the examination, your veterinarian should perform a complete exam to ensure there are not any surprises that may be hiding.  

The following things veterinarians recommend are fine needle aspirate of the mass to help make a definitive diagnosis. A fine need aspirate is placing a needle into the mass to obtain a sample of the cells. 

The sample is then placed on a slide which is stained and evaluated under a microscope.

Wait, wait, wait, Doc!! My veterinarian just had to feel the mass and told me it was a lipoma, and it was fine. They didn’t need to perform any additional testing and charge me more money. You just want veterinarians to make more money.

No, I want what is best for your pet along with your veterinarian. No human has microscopic fingers or hands that can definitively diagnose these bumps. At least I don’t think so, and if they do, they should be charging a lot more for this service.

Now please do not ask your veterinarian if they have microscopic fingers or hands. Also, realize that I do not mean to be disrespectful for these comments, but this is where veterinarian medical has evolved and the gold standard of care.  

Now back to my recommendations for lumps, bumps, and growths in your dog. Samples collected by your veterinarian will either be evaluated in-house or sent to an outside laboratory. Honestly, I prefer sending them to an outside laboratory to be assessed as there is a veterinary clinical pathology evaluating the slides.

A veterinary clinical pathologist has completed a residency to specialize in evaluating animal tissue and bodily fluids. These doctors have a more expansive knowledge than me with looking into a microscope and forming a diagnosis. I would want the most knowledgeable doctors on my team, and I like that for your pet.  

Photo by Viajero on

Word of Caution

A fine needle aspirate may not produce the answers we want or even give us answers to what a mass is. 

Sometimes a mass does not like to exfoliate or release its cells during the aspirate, or we may not hit the sweet spot. As veterinarians casually term it, the sweet spot is the mass area that is not surrounded by inflammation or infection.

If a fine needle aspirate comes back as inconclusive, your veterinarian may recommend further testing, including biopsy or removal of the mass with histopathology, to obtain a definitive diagnosis.

Step 2: What is my pet’s diagnosis, doctor?


If the results come back as benign growth, then you can choose your own adventure paths.

  • Monitor the growth. If you see any changes in size, shape, or texture, then have your veterinarian re-evaluate. A growth does not always stay benign and can become malignant over a pet’s lifetime.
  • Surgical removal because eeewww that growth makes Fluffy look so horrible!


If the results come back as malignant, I recommend having the growth surgically removed as soon as possible to lower the risk of spread to other parts of the body. Your veterinarian will also discuss staging to determine if there has been a spread of the tumor.  

With surgery, I also recommend the mass sent to the laboratory for histopathology. The importance of having the mass evaluated by the laboratory includes obtaining the mitotic index, checking margins, and confirming the diagnosis.

Mitotic index is stating how many mitotic cells are seen in a high-powered field. Mitotic cells are the ones that are dividing and wanting to make new cells. High numbers of mitotic cells indicate an aggressive tumor, while low numbers indicate a less aggressive tumor.

Margins of a surgically removed tissue mean we are looking to see if abnormal cells extend to where we cut. 

We also want to know the distance from our cut to the abnormal cells. This information tells us if we completely removed cancer and the likelihood it will return in this spot.

Inflammation or Infection

Whoo-hoo, it’s not cancer!! 

Your veterinarian will form a treatment plan to help resolve the infection and inflammation.  

Step 3: Staging a Malignant Growth

Staging of malignant growth is extensively evaluating the body to see if there is evidence of spread. 

Staging can include:

  • Bloodwork and urinalysis
  • Biopsy of the local lymph nodes
  • Chest X-rays
  • Abdominal ultrasound

Staging helps to determine the long-term prognosis and long-term treatment for your pet.  


Step 4: Long Term Monitoring

I recommend checking your pet every month for any new lumps, bumps, or growths. Make sure to journal any new growths indicating the date of when they were found, size, and texture. Recording this information can be helpful to your veterinarian. Additionally, monitor any previously diagnosed benign growths for changes that may indicate the need for re-evaluation.


It can be scary to find a lump on your pet. When I have found lumps on my pets, my brain immediately goes to the worst-case scenario. The best advice a veterinarian can give you is to have the bump checked out sooner rather than later. Malignant bumps start out tiny and can become giant, aggressive beasts, but if found early, they can mean a good prognosis for your pet.  

If you have any questions or concerns about your pet, I recommend contacting your veterinarian to discuss your pet’s case. Please also remember to be kind, patient, and courteous with your veterinary staff.  They love your pet as much as your do and want the best for our four-legged friends.  

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