Overview

Lipomas are one of the most common benign (non-cancerous) tumors in dogs and consist of fatty tissue (adipose). Lipomas are typically slow-growing, round, soft and movable, most often appearing as a lump under the skin. Although not all lipomas require treatment, surgical removal may be required to prevent them from growing too large, especially in locations that could interfere with limb movement.

Cause

The exact cause of lipomas is unknown, but certain groups of animals are predisposed, including older and overweight dogs and certain breeds such as Labrador Retrievers. 

Simple lipomas are benign and slow-growing, forming within a capsule, and are commonly found under the skin on the torso and limbs. However, they can also develop between muscles or, less commonly, on internal organs. Dogs may develop a single lipoma or multiple growths.

In contrast, infiltrative lipomas are less common and invade surrounding tissues such as muscles, bones and nerves. Although still benign, infiltrative lipomas tend to grow faster than simple lipomas and have a higher recurrence rate. 

A rare malignant tumor of fat cells is known as a liposarcoma. While liposarcomas do not tend to spread to other areas of the body, they often infiltrate the surrounding tissues.

Diagnosis

Your veterinarian may suspect a lipoma based on physical examination and palpation of the mass. However, additional testing is often recommended to confirm a diagnosis and rule out other common types of tumors that may feel similar. 

A minimally invasive test called a fine needle aspirate (FNA) may be recommended. This involves your veterinarian inserting a small needle into the mass to collect cells and examine them under a microscope. Alternatively, a biopsy (surgical removal of the mass) may be performed to confirm a diagnosis and, in some cases, simultaneously treat the suspected lipoma if it is removed in its entirety.

Treatment

Not all lipomas require treatment. However, surgical removal is typically curative for simple lipomas and can be performed with a relatively small incision. Your veterinarian might recommend surgical removal of the lipoma if it is located in an area like the armpit (axilla), as this could interfere with your dog’s normal limb movement.

Although lipomas typically grow slowly, they can become quite large over time. For this reason, your veterinarian may recommend removing a lipoma proactively before it reaches a significant size to prevent post-surgical complications, such as the formation of a large fluid pocket (seroma) in the space left after a large mass is removed. If not surgically excised, simple lipomas should be monitored for changes in size, firmness, or discomfort.

Unlike a simple lipoma, an infiltrative lipoma often necessitates a wide surgical excision to remove all tumor cells. Diagnostic imaging, such as a CT scan, may be recommended to assist in surgical planning or additional treatments like radiation therapy.

Outcome

The prognosis for simple lipomas after surgical removal is excellent, as they rarely recur after complete excision. However, new lipomas can develop in other areas. Your veterinarian should evaluate any new growths, as lipomas can resemble other types of tumors. 

Infiltrative lipomas and liposarcomas may be difficult to remove completely, increasing the risk of tumor regrowth. These types of lipomas often require larger surgical excision but can often have a good prognosis with complete removal. 

Updated March 2025