Q & A: Skin Tumors in Pets
By Dr. Kim Everson, DVM
Question: I just found a lump on my dog’s side. It wasn’t there a few weeks ago when I bathed him last. I’m really worried it could be cancer. What can I do about it?
Answer: Early detection of cancer is essential, so it’s a good thing you check your pet regularly and report any changes to your veterinarian. Fortunately, the majority of tumors you can feel on or just under the skin do not correlate to significant internal disease. However, the small proportion of skin masses that do spread to internal organs must be identified and removed quickly. Therefore, it is best to schedule an appointment with your veterinarian to have any new lump or bump checked out, especially if it is growing quickly, bleeding or otherwise bothering your pet.
After examining your pet and recording important qualities about the mass (which may include its location, size, shape, texture, depth, etc.) your veterinarian may recommend a screening skin test called a “fine needle aspirate (FNA) and cytology”. This test involves sampling the mass with a needle and looking at the cells under the microscope. The good thing about an FNA is it can be done on an awake pet because it does not cause significant discomfort; therefore, results are available quickly.
Certain tumors are easily identified by the FNA test. You may get good news that the mass is not serious and no further action is needed. However, sometimes the FNA test is inconclusive. If the mass cannot be identified by FNA, your veterinarian may recommend surgical biopsy for definitive diagnosis by histopathology. “Histopathology” is where a pathologist examines slices of the tumor under the microscope to determine with more accuracy what kind of tumor is present and how serious it is.
There are two general categories of surgical biopsy: incisional and excisional. Many skin tumors are surgically tested by “excisional biopsy” where the entire mass is cut off the pet and submitted for histopathology. Many times an excisional biopsy is not only diagnostic but also curative if the pathologist reports there are “wide margins,” or that healthy, non-cancerous tissue surrounds all edges of the removed tumor.
On the other hand, an “incisional biopsy” involves cutting out one or more small pieces of the tumor for histopathology. An incisional biopsy is generally done when the tumor itself is very large and/or invasive and cannot be easily or safely removed in its entirety. Once the tumor is identified, additional surgery or cancer therapy may be recommended such as chemotherapy, radiation therapy, etc. A veterinary “oncologist,” or cancer specialist, may be consulted at this point for exploration of all the available options.
The majority of skin masses that veterinarians see on a daily basis are readily identifiable through examination and FNA. Usually these masses are “benign,” or not harmful to the pet. Examples of benign masses include warts, skin tags, cysts, “lipomas”(a.k.a. fatty tumors), some eyelid tumors and several others. If a mass cannot be identified as benign by examination alone, it should be tested by FNA. Even lumps under the skin that feel soft and fatty may actually be found to be “malignant,” or dangerous to the life of the pet. Also, just because a pet has had previous lumps identified as benign by FNA does not mean that new lump is also benign. Of the 10 skin masses found on a given pet, 9 might be benign lipomas, but the 10th might a malignant tumor.
Malignant tumors vary in their seriousness. The worst malignant skin tumors spread, or “metastasize,” to surrounding lymph nodes and organs (including the lungs, liver, brain, spleen, etc.). These tumors usually result in death, but aggressive surgical and oncological care may extend the pet’s quality of life. Some malignant skin tumors are “locally invasive” meaning they do not spread throughout the body but may be difficult to completely remove from the original site. After attempted excisional biopsy, they may return months or years later, but may not directly result in a pet’s death.
Pets and people share many diseases and cancer is one of them. When it comes to skin cancer in pets, however, sun exposure is not as big a factor as it is in humans. Instead genetics, viral infections, lifestyle (i.e., obesity) and inflammation do seem to play a role in development of certain skin tumors in pets. Working closely with your veterinarian to map and identify your pet’s lumps and bumps as they arise can provide peace of mind and even a chance of a cure!
Originally printed in Pet Journal, March 2014