How To Tell The Difference Between A Fatty Tumor And A Cancerous Tumor On A Dog?

Lipomas and cancerous tumors can sometimes appear similar in dogs, but there are key differences. Lipomas are benign fatty tumors that commonly grow between a dog’s skin and muscle layer. They are soft, moveable lumps that feel like fatty tissue and are usually not harmful (Source). Cancerous tumors, on the other hand, can be malignant and invade surrounding tissue. They are often immobile, firm, and continue growing rapidly. While lipomas are usually harmless, cancerous tumors can be very dangerous if left untreated. It’s important for dog owners to monitor any new lumps or bumps and have a veterinarian evaluate them as soon as possible.


The most common symptom of a fatty tumor is a lump or bump under the skin. According to Zumalka, fatty tumors often appear as small, round lumps that feel soft and movable under the skin.

Fatty tumors tend to grow slowly over time. As Hugspetproducts states, they can range in size from very small to several inches wide. The lumps are usually soft, movable, and painless.

In contrast, cancerous lumps tend to be hard, fixed in place, rapid growing, and may be ulcerated or inflamed. They are more likely to be accompanied by symptoms like appetite loss, lethargy, and lameness according to veterinary professionals.


Fatty tumors, also known as lipomas, are most commonly found on a dog’s underbelly, chest, legs, or armpits. According to Denver Pet Vet, lipomas often develop just under the skin in areas with abundant fat deposits. In contrast, cancerous tumors can develop anywhere on a dog’s body, but are most commonly found on the skin, mouth, lymph nodes, chest or abdomen, according to PetMD. The location of a tumor can be an important clue in distinguishing between a benign fatty tumor and a potentially malignant cancerous growth.


Lipomas are typically smaller lumps that range from 2-10 cm in size (about the size of a grape to the size of an orange). According to VCA Animal Hospitals, lipomas usually do not grow over 10 cm in diameter (source).

Cancerous tumors, on the other hand, can often grow much larger, sometimes to the size of a dog’s head or beyond according to Blue Cross. Cancerous lumps tend to increase in size rapidly compared to benign fatty tumors (source).

So if a lump is very large, over 10 cm, or growing quickly, it is more likely to be cancerous than a benign fatty tumor. Smaller, slow growing lumps under 10 cm are more characteristic of benign lipomas.


Cancerous tumors tend to grow quickly, often doubling in size in a matter of weeks or months. This rapid growth happens as the cancer cells divide uncontrollably.

Fatty tumors or lipomas generally grow slowly over months or years. A lipoma has a defined edge and grows along fatty tissue planes, pushing aside muscle and skin rather than invading it. A lipoma may grow to a large size even though the rate of growth is slow. Most lipomas stop growing once they reach 2 to 3 inches in diameter.

If a lump is growing quickly, especially in a matter of days or weeks, it is more likely to be cancerous than benign. Consult a veterinarian promptly if you notice any fast-growing lumps or bumps on your dog. Source.


Lipomas are usually not painful. They tend to be soft, movable lumps under the skin, which do not cause the dog any discomfort or pain. However, if the lipoma grows very large, it can impinge on surrounding structures and nerves, which may cause some pain or irritation. The pain is often described as mild discomfort or itchiness in the area of the fatty tumor.

In contrast, cancerous tumors like mast cell tumors or hemangiosarcomas are often very painful. They tend to be hard, fixed masses that are firmly attached to underlying tissues. As they invade nerves and blood vessels, they cause significant pain and discomfort. Dogs with cancerous tumors may vocalize, lick or chew at the mass, or exhibit signs of pain like restlessness and aggression. So the presence of pain can help distinguish a benign lipoma from a malignant tumor.

However, it’s important to note that occasionally lipomas can also become painful if they rupture, bleed or get infected. And some malignant tumors may not be painful initially. So while pain can be an indicative sign, it should not be solely relied upon to differentiate between lipomas and cancerous tumors.


Although some lipomas are harmless, growths around joints or pressure points can restrict mobility and range of motion. Large lipomas can impede muscle function by compressing nerves and blood vessels. According to PetMD, lipomas on the elbows, armpits and groin often irritate surrounding tissue, while growths on the legs may make walking difficult and painful [1]. WebMD notes that lipomas on the ribs or torso can limit flexibility [2]. Pawlicy adds that rapidly expanding lipomas may crowd vital organs like the heart and lungs, impacting a dog’s stamina [3]. In severe cases, surgical removal may be required to restore mobility and quality of life.


If you notice a new lump or bump on your dog, the first step is to take your dog to the veterinarian for an examination. The vet will look at the location, size, texture, mobility, and appearance of the lump to get an initial idea of what it might be. However, the only way to definitively diagnose a fatty tumor versus a cancerous tumor is through a biopsy.

During the biopsy, the vet will use a needle to extract cells from the lump for examination under a microscope. This microscopic analysis allows the vet to determine if the cells are benign fat cells like those found in a lipoma, or if the cells are abnormal and cancerous (Benign Fatty Tumor or Cancer?, 2021). Sometimes, if the location of the lump allows it, the vet may recommend complete surgical removal of the lump for biopsy rather than just a needle biopsy.

In some cases, the vet may also recommend bloodwork or imaging tests like x-rays or an ultrasound to get a better view of the size, shape and internal structure of the lump. These additional tests can help determine if the lump is confined or if it is attached to surrounding tissues, which can aid in diagnosis.


Treatment for fatty tumors and cancerous tumors on dogs differs significantly based on the type, size, and location of the growth. Here are the main treatment options:

For small, benign fatty tumors that do not impede movement or quality of life, veterinarians often recommend observation and monitoring rather than removal. Since these tumors are typically non-cancerous, removal may be unnecessary if they are not bothering the dog. Periodic veterinary exams can check for any changes in size or symptoms.

Surgical removal is the most common treatment for larger fatty tumors or any malignant tumors. This involves surgically extracting the entire mass. The procedure is usually done under general anesthesia. Recovery time varies based on the location and invasiveness of the surgery. Possible complications include infection, recurrence, and fluid buildup, but these are relatively rare (

In some cases, a veterinarian may use cryosurgery (freezing) or laser surgery to destroy cancerous cells rather than full surgical removal. Radiation therapy is another option for malignant tumors in locations that are difficult to operate on.

Chemotherapy or immunotherapy drugs may be used alongside surgery to help prevent recurrence and metastasis of cancerous tumors. But chemotherapy has more side effects in dogs, so it requires close veterinary supervision.


The most important way to prevent fatty tumors in dogs is to make sure they maintain a healthy weight and have a nutritious diet. According to this source, obesity is one of the leading risk factors for developing fatty tumors. Feeding your dog a high-quality dog food formulated for their life stage, breed size, and activity level can help keep their weight in a healthy range.

Additionally, you should monitor their calorie intake and adjust as needed if they start to gain too much weight. Exercising your dog regularly will also help burn calories and prevent excess fat from accumulating. Try to limit unhealthy high-fat and sugary treats and table scraps. Sticking to the recommended feeding guidelines on their dog food packaging is a good way to control portions.

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