What’s This Lump on My Dog?

What’s This Lump on My Dog?

Recently a client came in with her wonderful dog, and she says, “I know I’m a crazy dog mom, but there’s this little lump on my dog I would like you to look at.”

First- you are not crazy for wanting the best care for your pet. I hope that you (any client reading this) know that’s why I’m here- to figure out what’s going on and to help find answers, solutions, and peace of mind.

Second- all lumps are SOMETHING. There are some lumps that are above the skin and I can say comfortably- this is a mole or wart- something benign that means we can watch it. Lumps that are in the skin or below the skin usually mean I need more information to give you an answer.

Let’s start with some vocabulary:

The medical term for lump is MASS, so I will use mass going forward to describe how we handle presentations for lumps.


The Webster’s medical definition is “not harmful.” How I explain that in terms of a mass is that it will not act aggressively toward your pet- it won’t spread to lymph nodes or the liver or the lungs.


Is basically the opposite. Malignant masses can be what is described as locally aggressive- meaning they like to take up as much space as they can where they are and cause harm to the tissues around them OR they can be malignant and spread far away from the mass and affect important anatomy such as the liver and lungs. Some masses are very malignant, others are slow. Knowing the type of mass is what gives me the power to tell you what to expect.

SOOOOO, you’re at the vet. You've discovered a small, soft mass on your pet—now what? Understanding the next steps is crucial in proactive pet care.

Step 1: Initial Assessment and Fine Needle Aspirate

  • The Process: I may not be able to make a microscopic diagnosis without a microscope, but I can gather essential information without immediate recourse to sedation or surgery. By using a needle and syringe, I can collect cells from the mass. This process involves extracting cells and expelling (or, less scientifically, 'squirting') them onto a slide for microscopic examination. This technique is known as Fine Needle Aspirate and Cytology (see photos 1A and 1B for reference).
  • What I Look For: Once the slide is stained, it highlights the cells' structure and characteristics, essential for diagnosis. I analyze the uniformity of the cells, their differences, and the extent of these differences. Additionally, a classification system helps determine the cells' type and, subsequently, the mass's potential behavior—benign or malignant.

Step 2: Diagnostic Cytology

  • Some cytology samples are diagnostic, meaning they allow me to identify the mass as a specific type of tumor and establish an approach for its management. Others indicate potentially worrisome cell populations, necessitating further action—like a biopsy, surgical excision, or additional diagnostics (X-rays, ultrasound) to check for any spread (see photo 2A and 2B showing the mass).

Step 3: Deciding on and Undergoing Surgery

  • The case in point: My client was proactive, leading us to a definitive diagnosis post-cytology. The mass required surgical intervention due to its cell type. These cells tend to spread locally, often beyond the visible mass's margins. Photos 3A and 3B illustrate the recommended surgical margins for this mass type's removal, while 3C shows the post-removal sutures. Timely action minimized the surgical site's size, demonstrating the importance of early detection and intervention.

Step 4: Histopathological Examination

  • After removal, the mass is sent for histopathological examination. This in-depth analysis enables the pathologist to view the tumor's architecture and verify whether it has been entirely removed. It’s also crucial for a definitive diagnosis and informs any further medical steps. Depending on the findings, these might include:
    • Confirmation of complete excision, potentially curative.
    • Monitoring for local recurrence.
    • Recommended chest X-rays to check for pulmonary metastasis.
    • Possible chemotherapy or radiation therapy protocols.

The Value of Proactive Pet Care

Being proactive in your pet’s health management, especially in situations like discovering a mass, is not an overreaction—it's responsible pet parenting. The sooner we identify and diagnose a mass, the quicker and more effectively we can address it. Embracing proactive pet care means providing your pets with the thorough, compassionate care they deserve. So, please, never feel self-conscious about being a “crazy” pet parent—it's simply a sign of your commitment!

- Dr. Carlton