When I discovered a lump on your cat Toby’s jaw, my heart sank. I reasoned it was cancer. Pets, on the other hand, can develop a variety of benign or easily treatable lumps and bumps.
My pets have developed allergies, acne, fatty tumors, and even an inverted nipple on my cat Kura.

The most important thing to do is to talk to your veterinarian. You and your veterinarian will be able to decide which diagnostic tests to perform and what treatment plan is best for your pet.
Here are some of the lessons I’ve learned from my own pets:
Any lumps or bumps should be examined by a veterinarian. If the tumor is cancerous, catching it early gives your pet the best chance of beating it. If the lump is benign – or something else entirely – your veterinarian may have treatment recommendations and can advise you on what to do if a similar lump appears again.
“A vet will want to know when you first noticed the mass, if it’s changing, and if it’s bothering your pet,” explains Dr. V, a veterinarian and Pawcurious blogger. “They’ll also want to know if you’ve had any previous masses removed or biopsied.”
Prepare for exams. Without performing some sort of diagnostic test, no veterinarian, no matter how skilled, can provide you with a definitive diagnosis of a lump on your pet’s skin. “I assumed Kekoa [Dr. V’s dog] had a simple lipoma, which is a common benign fatty tumor,” Dr. V says. “However, just to be sure, I biopsied it, and it turned out to be an aggressive sarcoma.” “I’m so happy I did!” More than a year after treatment, Kekoa’s cancer has not returned.

Inquire about the test(s) that your veterinarian has recommended. The questions you ask your veterinarian can help you figure out what you’re up against and whether you need more tests. Here are some suggestions to get you started:
- What types of lumps and bumps are common in this age group of pets?
- What types of masses are common in this area of the body of a pet?
- Do you believe any organs, bones, or tissue are involved?
- Do you have any recommendations for additional tests?
- What are the worst-case and best-case scenarios?
- Would you give a biopsy to your own pet? If so, what kind?
- How precise is your proposed procedure?
- Is my pet in any distress?
- Will a clear diagnosis change the treatment plan?”

Recognize the various types of tests. A cautious veterinarian will almost certainly want to examine a piece of the lump under a microscope to determine what types of cells are present and whether they are cancerous. Here are some ways your veterinarian might collect a sample:
- Smears with a sterile microscope slide: If the mystery bump is oozing or fluid-filled, or if your veterinarian can easily obtain a sample of the mass, she may choose to dab a sterile microscope slide on it. The slide is usually reviewed by a veterinary pathologist, but the diagnosis is sometimes made by an attending veterinarian, according to PetMD.
- Dr. V. describes aspirations/fine-needle biopsies as “a small needle is introduced into the mass, usually while the animal is awake, and some cells are removed.” “Typically, this is a simple, minimally invasive procedure that does not require sedation.” It is not as precise as true biopsies, but it can serve as a good starting point. I’ve diagnosed mast cell tumors, lymphoma, and a variety of other serious cancers using this simple procedure.”
- Incision and/or punch biopsies: Your veterinarian may recommend removing a small piece of the lump while your pet is sedated, depending on the location of the mass, its size, shape, and other factors. The vet needed to take a sample of the mass from inside Toby’s mouth, which Toby refused to do while he was awake! Your veterinarian may request blood work before putting your pet under anesthesia to ensure that he or she is healthy enough. She may also suggest that you get an x-ray or a CT scan to get a better look at the mass.
- Excision biopsies involve the removal of the entire mass and examination under a microscope. Like incision biopsies, these procedures usually necessitate general anesthesia and all of the same pre-anesthesia diagnostics. (In Toby’s case, x-rays of his jaw revealed that the mass was attached to his jaw bone, making an excision biopsy risky and difficult.)

A procedure will be recommended by your veterinarian based on a number of factors, including the length of time the lump has been present, its shape and size, and whether there have been any recent changes.
Excision biopsy may be the most cost-effective option if your pet is already scheduled to be sedated for another procedure. Some masses, however, must be removed differently than others, so if you choose an excision biopsy, be prepared for a second excision if the results indicate that one is necessary. “For example, a mast cell tumor requires 3-cm. margins all around,” says Dr. V. “Even for a small mass, that’s a lot of twill to get rid of!” If you performed an excisional biopsy, assuming it was for something else, you may need a second procedure to obtain surgical margins if pathology revealed that the margins were not clean.
Consider how important the information is to you. This is a question only you can answer. Tests are expensive, anesthesia is risky, and asking the questions above can sometimes give you a good idea of what you’re dealing with without performing diagnostics. Furthermore, having a definitive diagnosis may not change your veterinarian’s recommended treatment plan in some cases. (Having pet insurance is a great way to avoid having to factor in as much cost.)
We knew Toby had an aggressive form of cancer with few treatment options even before the biopsy. But I knew that if we didn’t run the tests, I’d be left wondering if we’d missed something else – something treatable. A biopsy was performed, and my worst nightmare came true: it was cancer. Nonetheless, the early diagnosis gave me a clear plan of action and allowed his veterinarian and me to do everything possible to keep him comfortable. When Toby passed away earlier this year, I said my final farewell knowing I’d done everything I could – and it’s helped me enormously as I learn to live without him.
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