Mass Destruction: Battling Lumps and Bumps in Pets

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*Written by Rebecca Risbon, DVM. Article concept and editing by Holly Russel.

If veterinarians are our superheroes, then illness is the villain. And of all the signs of sickness out there, one stands apart as a pet’s arch-enemy: the unidentified mass. As furry friends age, various lumps and bumps can break out on the skin surface and from the tissues under the skin. Some can be completely benign, while others require help from higher places. How do you know when it’s time to put up the Bat-Signal? Here’s veterinary oncologist Dr. Rebecca Risbon’s guide to the Bad Guys.

The Riddler (lipomas)
Lipomas can be puzzling at first; they look like tumors, but are actually completely benign. Lipomas arise from fatty tissue and are soft and freely movable under the skin. They do not spread to other locations in the body and do not transform into a malignant version. Many times lipomas can be monitored without the need for surgical intervention. However, they can grow quite large and depending on the location, may begin to affect the ability to walk.

A more invasive version, called an infiltrative lipoma, can invade into the surrounding tissues and needs to be addressed with surgery and possibly radiation therapy.  Any lump that starts out soft and freely movable should be closely monitored and examined immediately if it changes character.

Two-Face  (mast cell tumors)
Mast cell tumors arise from immune system cells (mast cells), which contain histamine and are normally responsible for allergies. They can take on any appearance: raised, ulcerated or hairless, and can arise above or under the skin surface. We do not know their true cause, but they are the most common skin tumor in dogs.

One characteristic feature of mast cell tumors is that they can swell and shrink repeatedly due to histamine release when they are touched or bumped. They can be curable with surgery, but can also become very aggressive, spreading to the lymph nodes, liver and spleen. The best recommendation if you suspect a mast cell tumor is to have your veterinarian make the diagnosis with a needle aspirate followed by removal and biopsy for more information. Further treatment will depend on specific features described on the biopsy.  Approximately 20-40% of dogs that develop one mast cell tumor will develop another in the future, so any new lump should be evaluated immediately.

Cats can also develop mast cell tumors in the skin (particularly Siamese cats). They are more commonly located on the head and neck and can be hairless and white or pink in color. Some forms of cutaneous mast cell tumors will spontaneously regress while others need to be removed with surgery. The treatment recommendation for cats with mast cell tumors is similar to that for dogs.

The Joker (squamous cell carcinomas)
Squamous cell carcinomas are no laughing matter. Caused by UV light exposure, they arise from the epidermis and are common on lightly haired areas of the head like the tips of ears, eyelid margins and nose. They often appear as a plaque-like lesion with surrounding redness and crusting. White cats and lightly colored dogs are vulnerable to squamous cell carcinomas and any crusted lesion in either species should be evaluated promptly.

Doctor Octopus (sarcomas)
Tumors arising from the tissue holding our body together, called soft tissue sarcomas, all have a similar behavior: they are locally invasive and often have tendrils that invade into the deeper tissue, making complete removal difficult. The tumor is typically firm and fixed to the underlying tissue rather than freely movable and soft like lipomas. A biopsy is often required to diagnose these tumors and to determine if any additional treatments are needed following surgery. Local treatment is usually all that is needed, as the chances of cancer spread are minimal unless the tumor is determined to be aggressive based on the biopsy.

Cats are prone to developing sarcomas following vaccinations or injections. This specific type of sarcoma, called an injection site sarcoma, has gained attention since the late 1980s and early 1990s. It appears that the sarcoma is caused by the individual cat’s inappropriate or excessive immune response to the vaccination or injection. Therefore, we cannot predict in advance which cats are potentially at risk.

Because injection site sarcomas are locally aggressive and have the potential to spread, any lesion that develops near the site of an injection should be evaluated according to the 1-2-3 rule: any lesion increasing in size more than 1 month after vaccination, larger than 2cm, and still evident 3 months or more after vaccination should be addressed. Our efforts are directed at prevention, as they can be very difficult to effectively treat. Improved vaccination schedules and protocols have helped reduce the incidence of these tumors.

beating the bad guys
No matter the lump or bump, any new growth on your pet should be evaluated by a veterinarian to determine whether treatment is indicated. Your vet should evaluate any mass that:

  • develops suddenly
  • grows quickly
  • changes character or shrinks and swells
  • arises at an injection site
  • is firm and fixed to the underlying tissue
  • is ulcerated or bleeding
  • concerns you

The best chance to vanquish masses is to tap into your veterinarian’s superpowers. Early detection can lead to improved outcomes—and maybe even save your pet’s life.

— published in fetch! magazine, the “Bumps in the Road” issue

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