Common Skin Tumors in Cats
The skin is the largest organ of the body. Because it is constantly exposed to many cancer-causing factors in the environment, such as UV rays, chemical carcinogens, and viruses, skin tumors are the most commonly diagnosed tumors in cats. Keep reading to learn about the most common types of skin tumors in cats and how to recognize when there might be a problem.
Benign vs. Malignant Skin Tumors
Feline skin tumors can be benign or malignant (cancerous). Benign skin tumors don’t metastasize (spread) to other areas of the body. They don’t have invasive properties and can be removed easily with surgery. On the other hand, malignant tumors can invade surrounding tissues and spread to organs that are far from the point where the tumor originated (metastasis).
In a study that documented skin tumors in 340 cats, 26% were identified as basal cell tumors, 21% mast cell tumors, 15% squamous cell carcinoma, and 15% fibrosarcoma. These types of tumors comprised 77% of all the cases. The number of cases was highest in cats older than 10 years of age. Mast cell tumors were the only tumors diagnosed in cats younger than one-year-old. The most common site for the development of basal cell tumors, squamous cell carcinomas, and mast cell tumors was the head of cats. The most common site for fibrosarcomas was the legs.
Types of Skin Tumors in Cats
1. Squamous Cell Carcinoma (SCC)
Squamous cell carcinoma affects the cells on the outermost layer of the skin known as the epidermis. It can occur as a solitary tumor or it can be multicentric (spread over various areas of the body). The latter is characterized by the occurrence of two or more tumors in several areas of the cat’s body including the mouth. Multicentric SCC is also called Bowenoid carcinoma or Bowen’s disease. Cases of multicentric SCC in cats are rare and often develop in sun-damaged areas of the skin.
The ultimate cause of squamous cell carcinoma development in cats has not been fully established. But several important predisposing factors can increase a cat’s risk of developing this type of skin tumor. These include:
- Environmental factors - most common examples are exposure to ultraviolet rays of the sun, chemical carcinogens, papillomavirus, etc.
- Genetic or hereditary factors - cats with white or light-colored hair coats have a higher risk of getting these tumors. The most commonly affected areas include the ears, eyelids, nose, and lips.
At first, squamous cell carcinoma in cats appears as small sores that don’t heal. With time, most become raised and irregular growths that may have open sores.
This type of tumor is highly invasive to the other parts of the body, including the surrounding bones and tissues. Because of the tumor’s invasive nature, early detection and medical attention are critical for a favorable prognosis.
2. Mast Cell Tumor (MCT)
Mast cells are a type of white blood cell which is part of the immune system. A mast cell tumor (MCT) is composed of mast cells. It can form abnormal growths or nodules in the skin or internal organs. There are two types of MCT:
- Cutaneous mast cell tumors affect the skin and account for approximately 20% of skin tumors in cats. About 90% of cutaneous MCTs are benign. They are generally found on the cat’s head and neck but can also affect other parts of the body.
- Visceral mast cell tumors occur in the internal organs. About half of MCTs affect the visceral organs.
Cutaneous MCTs appear as small, firm, elevated growths that are itchy. Persistent scratching and chewing on the tumor can inflict self-trauma. Growths that get suddenly larger and then smaller over a 24-hour period are likely to be mast cell tumors, and this phenomenon is referred to as Darier's sign.
MCTs are very invasive and difficult to treat. The surgical removal must be broad and deep because the true margins of the tumor cannot be seen with the naked eye. When caught early and given prompt treatment, cats with cutaneous MCTs have a favorable prognosis and most live for many years after the surgery. MCTs are not very likely to re-occur after surgery.
Although MCTs can affect cats of any breed or age, it is more common in cats over 4 years old. There is also a higher incidence of MCTs in Siamese cats.
Fibrosarcomas affect soft tissues of the body, but the most commonly affected organ is the skin. It is a locally aggressive type of cancer that is slow to metastasize.
This malignant tumor is caused by a combination of environmental and genetic factors. Although a specific cause has not been identified, many cases of feline fibrosarcoma occur in vaccination or injection sites. Vaccine-associated sarcomas often develop in the connective tissue layer between the skin and muscle. Fibrosarcomas usually develop long after vaccination has been performed.
Generally, fibrosarcomas don’t cause any pain or discomfort. If a lump forms at the site of a vaccination injection, you should let your vet know. Biopsy should be performed in the following circumstances:
- If the lump has been present for more than three months
- The size of the mass is greater than 2 centimeters
- The mass has increased in size a month after vaccine injection
4. Basal Cell Tumors (BCT)
Basal cell tumors are common in senior cats. Some feline breeds like Persians, domestic longhairs, and Himalayans are more at risk. Tumors may occur anywhere on the cat’s body but are often on the head, neck, or shoulder.
They generally appear alone, firm, pigmented, and often hairless. However, basal cell tumors can also appear as ulcerated lumps that stick out from the cat’s skin surface. They can vary in diameter from less than an inch to more than four inches. While these cells are benign, some basal cell tumors can grow rapidly and may become ulcerated and inflamed. When this happens, surgical removal is often indicated.
Although most BCTs are benign, these tumors can continue to grow without surgery. Bigger tumors have greater chances of becoming ulcerated, infected, and are difficult to remove. Surgical removal of a basal cell tumor significantly contributes to an excellent prognosis.
5. Dilated Pores of Winer
While rare, these hair-follicle growths can occur in senior cats. Males are thought to be more predisposed than females. These large, blackhead-like growths most often develop on the cat’s head. These growths are benign and can be completely removed with surgery.
6. Lipoma (Fatty Tumors)
Lipomas may develop anywhere on a cat’s body. Older or overweight cats are often affected but these tumors can also be seen in cats of all ages and body conditions. Lipomas aren’t cancerous and surgical removal is usually not needed except when they impede your cat’s movements.
How Skin Tumors in Cats are Diagnosed
Diagnosis is generally made based on the physical appearance of the tumor. Your vet may choose to perform fine-needle aspiration (FNA) and cytology. The procedure involves the removal of a small amount of tissue from the tumor for microscopic examination.
Treatment of Feline Skin Tumors
The treatment for skin tumors in cats will depend to a large extent on the type of tumor, its location, size, and overall physical condition of the cat.
Benign skin tumors that are not ulcerated and don’t interfere in the cat’s normal routine are often left alone. However, if a tumor inhibits the cat from doing normal activities or appears cosmetically unpleasant, your vet may talk to you about several available treatment options. These include:
- Surgery - this option is the most effective, least expensive, and has fewer adverse effects.
- Laser and cryotherapy (freezing) - ideal for benign skin tumors that are small and superficial.
- Radiation treatment
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