Can Lipomas In Dogs Turn Cancerous?

A lipoma is a benign (noncancerous) fatty tumor that grows slowly beneath the skin (Lipoma Definition & Meaning – Merriam-Webster). Lipomas are typically soft, movable, and painless lumps that form gradually on tendons, muscles, and other soft tissues. They rarely grow larger than 2 inches in diameter. Lipomas are very common, especially in middle age and older adults, but they can develop at any age. Though usually harmless, in rare cases lipomas can press on nerves and cause pain or other symptoms. Removing them surgically is an option if they become bothersome.

What are Lipomas?

Lipomas are benign fatty tumors that commonly develop in older dogs, usually under the skin (Szanecki et al., 2017). They form from fat cells that clump together to create a soft, movable lump. Lipomas are typically slow-growing and range in size from a pea to a few inches across. They are usually soft, squishy, and not attached to surrounding tissues.

Lipomas are the most common type of skin mass found in dogs, especially in overweight, middle-aged to senior dogs. They can develop anywhere on the body but are most often found on the torso, shoulders, legs and armpits (iMedicalSociety). While lipomas are benign and usually don’t impact a dog’s health, occasionally they can become problematic depending on their size and location.

What Causes Lipomas?

The exact cause of lipomas is unknown. However, there are some factors that may increase the risk of developing them.

Genetics may play a role, as lipomas tend to run in families. People who have family members with lipomas are more likely to develop them.

Lipomas also appear to be associated with obesity and high cholesterol levels. Obese individuals and those with high cholesterol have a greater chance of developing lipomas.

While the exact mechanisms are unclear, it’s believed that genetics, obesity, and high cholesterol may all contribute to abnormal fat cell growth and proliferation, leading to lipoma formation.

According to the Cleveland Clinic, some additional potential causes include trauma or injury to soft tissues and abnormal development of fat cells.

Can Lipomas Become Cancerous?

Lipomas becoming cancerous is extremely rare, occurring in less than 0.3% of cases (Charifa, 2022). In very few instances, a lipoma can transform into a liposarcoma, which is a type of cancerous tumor that develops from fat cells. Liposarcomas tend to be larger in size and deeper than benign lipomas. They may feel firm or solid rather than soft or doughy like a typical lipoma.

Some signs that a lipoma may be becoming cancerous include:
– The lump is rapidly growing in size
– The lump becomes painful or tender

– It feels firm or hard
– Redness or inflammation develops on the skin above it
– You notice discharge coming from it

While the chances of a lipoma becoming cancerous are extremely low, it’s important to monitor existing lipomas and point out any changes to your veterinarian. Catching a cancerous liposarcoma early can make treatment more straightforward and improve outcomes.

Lipomas are generally benign, but there are some signs that can indicate if a lipoma has become cancerous. Cancerous lipomas, known as liposarcomas, require prompt medical attention.

Signs of Cancerous Lipomas

There are three key signs that a lipoma may have progressed to a cancerous liposarcoma:

Rapid growth – Benign lipomas tend to grow slowly over years. A lipoma that rapidly enlarges in weeks or months may be cancerous. According to the Mayo Clinic, a liposarcoma can grow to be over 20 cm (8 inches) in diameter (source).

Ulceration – Benign lipomas are smooth and moveable under the skin. An ulcerated lipoma that bleeds or oozes can indicate cancer. According to the Cleveland Clinic, ulceration occurs when the tumor grows through the skin (source).

Invasion into surrounding tissues – Unlike benign lipomas that do not invade other tissues, liposarcomas can spread into muscles, bones and other structures. This invasion can cause pain and impair limb function, notes the Mayo Clinic (source).

Diagnosing Lipomas

If you notice a lump or bump on your dog, the first step is to take your dog to the veterinarian for an examination. The vet will perform a physical exam, looking at the size, shape, location, and feel of the lump. They will also take your dog’s full medical history into account.

For most lipomas, a physical exam is often enough for a veterinarian to make a diagnosis. The typical lipoma is soft, movable, and located just under the skin. However, some lipomas can feel firmer and be more deeply rooted under the skin or muscle.

In cases where the lipoma is in an unusual location or has an atypical feel or appearance, the vet may recommend getting a sample of the cells for microscopic examination. This procedure is called a fine needle aspiration and involves using a small needle to extract cells from the lump for analysis. This can help rule out cancer.

If the lump appears suspicious, a biopsy may be recommended to examine the cells and confirm whether the growth is benign or malignant. Unlike fatty lipomas which have a very low chance of being cancerous, a type of lipoma called an atypical lipoma has a higher risk of malignancy, so a biopsy is often advised.

Imaging tests like x-rays, CT scans, or MRI scans may also be used to evaluate the extent of the lipoma, especially for those that are large, growing quickly, or located internally rather than under the skin.

Treating Benign Lipomas

Benign lipomas usually do not require any treatment unless they are causing discomfort, impairing mobility, or are growing rapidly. Since they are non-cancerous tumors, benign lipomas are not a medical emergency.

In most cases, veterinarians will recommend leaving benign lipomas alone unless they become problematic. Your vet will monitor the size and growth of lipomas at regular checkups. If a lipoma interferes with your dog’s mobility or quality of life, your vet may recommend surgical removal.

Surgical removal of a benign lipoma is a relatively simple procedure. Your vet will numb the area around the lipoma and make an incision to remove the fatty tumor. The tissue is sent to a lab for testing to confirm it is benign. Your dog will have dissolvable stitches and recover quickly after surgery.

While benign lipomas can often be left alone, it’s important to monitor their size and have any rapidly growing lumps examined. Catching a lump early on increases the chances of successful treatment. Have your veterinarian evaluate any new lumps or bumps on your dog during annual exams.

Treating Cancerous Lipomas

If a lipoma is found to be cancerous, more aggressive treatment will be required. Surgery is often the first option to remove the tumor. The veterinarian will attempt to remove the entire mass with clean margins to reduce the chance of recurrence.

Chemotherapy may be recommended after surgery to kill any remaining cancer cells. Common chemotherapy drugs used for dogs include doxorubicin, carboplatin, and cisplatin. Radiation therapy uses high-energy radiation targeted at the tumor site and may also be used to kill cancer cells post-surgery.

The treatment plan will depend on factors like the size and location of the tumor, whether it has metastasized or not, and the dog’s overall health. Close monitoring, including regular physical exams, bloodwork, and imaging tests, is crucial to watch for recurrence or spread of the cancer after treatment.

The prognosis for malignant lipomas varies widely based on the individual case. Early intervention, clean surgical margins, and adjuvant therapy like chemo or radiation can help improve the outcome. But in general, the prognosis for dogs with liposarcoma is guarded to poor depending on the stage and grade.


Preventing Lipomas

There is no definitive way to prevent lipomas from developing in dogs. However, maintaining a healthy weight may help reduce the risk. Overweight and obese dogs tend to develop lipomas more frequently than dogs at an optimal weight. Feeding a nutritious diet with appropriate calories for your dog’s needs, along with regular exercise, can help keep excess weight in check and potentially lower lipoma risk. There are no specific diets or supplements proven to prevent lipomas, but providing balanced nutrition supports overall health. While lipomas can’t always be prevented, keeping your dog fit and trim may help reduce the chances of these fatty tumors developing.

When to See the Vet

Most lipomas in dogs are benign and do not require any treatment. However, there are some instances when you should take your dog to the vet:

  • The lipoma is growing rapidly – Lipomas that suddenly increase in size should be evaluated by a vet. Rapid growth may indicate the lump is becoming cancerous (VCA Animal Hospitals).
  • The lipoma changes texture – Benign lipomas are soft and movable under the skin. If a lipoma becomes firm, immobile, or develops an irregular surface, it could be a sign of cancer (WebMD).
  • The lipoma impacts your dog’s mobility or quality of life – Lipomas that interfere with movement, sitting, walking, or otherwise affect your dog’s normal activities should be evaluated by a vet. Removing problematic lipomas can greatly improve comfort and mobility.

Schedule an appointment with your veterinarian if a lipoma shows any concerning signs of growth or change. Early evaluation and treatment provide the best prognosis if a lipoma does become cancerous.

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