Have you ever felt a lump under your dog’s skin? Quite commonly, masses develop in dogs. While the mass may be a benign fatty tumor, it may also be a cancerous lump. Less frequently, cats grow masses under the skin. However, if you discover one, it is much more likely to be cancer.

Benign Fatty Tumor

A benign fatty tumor (also known as a lipoma) is especially common in middle aged to older dogs. These can feel soft and are often freely movable underneath the skin.

Cancerous Masses

Generally speaking, cancerous tumors differ from benign tumors in that they are firmer, quickly growing and cannot be moved freely from other surrounding structures. Further, they may have an ulcerated surface


The only definitive way to determine if a mass is cancerous or benign is to have it examined by a veterinarian. If you find a new mass on our pet, please have you veterinarian evaluate it. To do so, your vet may perform a test called a fine needle aspirate. During this biopsy procedure, a veterinarian or veterinary technician will guide a small needle into the mass to collect some cells. The cells are then carefully spread on a slide and evaluated under a microscope. The vet may be able to diagnose the cells or s/he may send the slides to a veterinary pathologist for further evaluation.

Treatment of a Benign Fatty Tumor

The treatment of lipomas varies based on each patient’s needs. Many dogs merely need monitoring as these masses are benign, and often do not go on to cause a problem for the pet. Pets may develop multiple lipomas in different areas of the body. If the lipoma is growing, is in a high motion area or is bothering the pet, surgery to remove it may be recommended. Following surgery, the mass should be submitted to the pathologist to determine the definitive diagnosis.

Cancerous Masses

Masses that are more concerning for cancer are often more frim, quickly growing, may have an ulcerated surface, and cannot be moved freely from other surrounding structures. An aspirate is warranted on any mass that is detected on your pet.


The oncology team at CARE is passionate and compassionate about treating dogs and cats who are battling cancer. If your primary vet diagnoses your pet with cancer, ask for a referral to CARE. We will work with you and your family vet to come up with the best course of treatment.

Want to receive monthly notifications when we post on our blog? Subscribe here.