What Do Dog Cancer Masses Feel Like?

What does cancer look and feel like?

In short, it can look and feel like anything. 

These skin tumors can feel soft or firm, they can be covered in fur, ulcerated or hairless, they can also be painless, itchy or uncomfortable.

Sure, there are some types of skin masses (types of tumors) that tend to have a distinct appearance, where we might say "oh, that looks like a mast cell tumor" or "that's probably a soft tissue sarcoma". Then we take a sample (needle aspirate) to establish a diagnosis and make sure we're correct. 

Where we can get into trouble is when we presume that a tumor is benign because it looks and feels like a lipoma (or skin tag). We never want to make the mistake of assuming a tumor is benign, just by looking at it or feeling it. We need to sample all tumors to establish an accurate diagnosis.

A lipoma is a benign (cured with surgery) tumor of fat that feels soft and lives under the surface of the skin (in the subcutaneous tissues). As long as a lipoma is small and not bothering the dog, we typically don't feel that surgical removal is required.
**Note, there are other types of lipomas (infiltrative and intermuscular) that behave more aggressively, but the vast majority will be the traditional type as described earlier in this paragraph.

Often, a veterinarian will feel a skin mass and assume that it's a lipoma because it's soft and located in the subcutaneous tissues (just under the skin's surface). This is a mistake. It's critical to sample every lump and bump using a simple needle aspirate technique to determine if a tumor is benign or malignant. 

Some tumors (subcutaneous mast cell tumors for example) look and feel exactly the same as lipomas. The only way to distinguish between the two is with a needle aspirate. 

With a needle aspirate, a small needle is inserted into the tumor (usually a veterinary nurse is giving lots of pets and love during this time so the patient doesn't realize it's happening), cells are extracted and smeared onto a glass slide. If the tumor is a lipoma, the cells will look like shiny fat on the slide, and a diagnosis can be made on the spot. This procedure takes less than 2 minutes.

 If we do not see what appears to be fat on the glass slide, then the veterinarian should submit the slides to the pathology lab for an accurate diagnosis.

Similarly, mast cell tumors (cancerous) can look exactly the same as a skin tag. Most skin tags are too small for successful aspiration (the needle will go right through the tissue and will not collect cells), so a small biopsy is needed for accurate diagnosis in these cases.

What about a tumor that has been small for years? Is this benign?

Some dogs will have small tumors that have been present for years and that have not increased in size. 

These tumors may be benign, but they may also be malignant (cancerous). Again, the only way to know is to take a sample (aspirate).

We see this with many low-grade soft tissue sarcomas. These are low-grade cancers, that if treated appropriately, are typically associated with long-term survival (the patient should live for years after successful surgery).

I often have clients that come in for a tumor that was stable for years, but recently became quite large. 

This can be confusing because they thought they were monitoring a benign tumor.

In some cases, a low-grade soft tissue sarcoma will stay small for years. Then the cancer cells will mutate and become more aggressive (become a higher grade tumor), at which point the tumor will increase in size rapidly. Unfortunately, higher-grade tumors are difficult to control and can lead to the death of the patient. 

These cases are heartbreaking because if the original low-grade tumor was sampled and removed, the patient would not have been expected to die from that disease. Once the tumor becomes high grade, the story changes.

What about a skin tumor that goes away and comes back?

Does your dog have a skin tumor that seems to have magically disappeared then reappear again? Has this happened more than once? 

This is a common feature of mast cell tumors (MCT). If the tumor becomes irritated by licking, scratching, poking, bathing, etc. histamine will be released from within the tumor cells causing the tumor to appear temporarily larger. When this happens you can circle the tumor with a black marker so your veterinarian will be able to find it later and make a diagnosis. 

General recommendations...

In general, we recommend sampling all lumps and bumps using needle aspirate to establish a diagnosis. 

Obviously there are exceptions to every rule (ex. if you have a geriatric dog with another life limiting condition), but those should be discussed with your oncologist (or general practitioner).

Have questions about this article? Reach out!

Dr. Lori Cesario
Board Certified Veterinary Oncologist
lori@caninecanceracademy.com 


A few other articles you might enjoy...

(1) How to Assess Pain and Quality of Life in a Dog with Cancer 
(2) 6 Steps To Get The Most Out of Your Oncology Consult!
(3) Help! What Are They Talking About? (Part 2)

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