Lipomas in Dogs Look Bad, But Aren’t That Bad

What is lipoma?

A lipoma is a term to describe a prevalent benign tumour of fat seen in middle-aged to older dogs. These tumours can vary in terms of their growth rate (some may remain the same size for years) but become problematic for your pet when they grow in locations that impact their ability to walk or cause discomfort. Lipomas can grow anywhere (even inside the abdomen), but the most commonplace is under the skin, where fat is usually present. They may grow in between layers of muscle or may grow in a location that causes your pet discomfort whenever they walk. When these tumours grow between muscle layers, they are typically called infiltrative lipomas.

The malignant form of this tumour is called liposarcoma. These tumours tend not to spread to other places.

What causes this type of tumour?

The reason why a particular pet may develop this, or any tumour or cancer, is not straightforward. Very few tumours and cancers have a single known cause. Most seem to be caused by a complex mix of risk factors, environmental and genetic or hereditary.

How are these types of tumours diagnosed? 

Typically, these types of tumours can be diagnosed by fine-needle aspiration.

FNA involves taking a small needle with a syringe, suctioning a sample of cells directly from the tumour, and placing them on a microscope slide. A veterinary pathologist then examines the slide under a microscope.

In some cases, results from FNA may not be entirely transparent, and biopsy may be necessary. A biopsy is a surgical excision of a piece of the tumour. A veterinary pathologist then examines details of the tumour under the microscope. This is called histopathology. Histopathology helps make a definitive diagnosis. Advanced imaging (such as a CT scan) may also be recommended.

How do these types of tumours typically progress?

Although lipomas are benign, meaning they are not cancerous and will not spread (metastasize) to the surrounding tissues or internal organs, without surgery, tumours may continue to grow, causing your pet discomfort. Once removed, the likelihood of recurrence is relatively low. However, it is widespread for middle-aged to older dogs to have multiple masses suspected to be lipomas. Every lipoma is different; some may increase, and some may take years to grow large enough to be of concern.

Liposarcomas, however, are malignant and have a much higher recurrence after treatment, meaning multiple attempts at treatment may be required. In addition, the spread of liposarcoma is possible, although rare. Typically, liposarcomas are treated more aggressively.

How will this type of tumour affect my dog?

In benign lipomas, removal of these masses is more cosmetic than anything. Some pets will develop these tumours in their armpit region, between their legs, or around the neck, which can cause discomfort and lameness. You may see your pet exhibit an irregular gait, reluctance to stand or walk upstairs, or go for their regular walks.

What are the treatments for these types of tumours?

The single most effective treatment for lipomas is surgical removal. It is best to remove these masses when they are small; the surgery is usually less invasive, and the incision will be much smaller/less painful for your pet. As lipomas grow, the surgery may become more difficult for both your veterinarian and your pet.

Infiltrative lipomas and liposarcomas that have recurred after surgery commonly recur and need to be surgically removed again. Post-surgical radiation therapy may be recommended for recurrent liposarcomas or infiltrative lipomas.