Surface tumors are common in cats. It is often impossible to determine whether a surface tumor is benign or malignant by appearance alone. The only conclusive way to make a diagnosis is by biopsy, a procedure in which tissue or cells are removed by your veterinarian and examined under a microscope by a veterinary pathologist.
For small tumors, it is best for your veterinarian to remove the growth and present the entire specimen to the pathologist. For tumors larger than 1 inch (25 mm) across, it may be advisable for your veterinarian to obtain a tissue sample by fine needle aspiration. In this procedure, a needle connected to a syringe is inserted into the tumor and cells are obtained by pulling back on the plunger. Alternatively, the vet can use a cutting needle to obtain a core sample. An open biopsy, in which an incision is made, is preferred for suspected sarcomas and tumors that present diagnostic problems for the pathologist
Epidermal Inclusion Cysts (Sebaceous Cysts/Keratin Cysts)
Epidermal inclusion cysts, also called "sebaceous cysts", are benign tumors that arise from glands found beneath the skin. They can occur anywhere on the body. Although less common in cats than in dogs, they are still the most common surface tumor in cats.
A sebaceous cyst may be made of a thick capsule that surrounds a lump of cheesy material containing keratin. It may grow to 1 inch (25 mm) or more. Eventually, it is likely to become infected and will have to be drained. This sometimes leads to a cure.
Treatment: Most cysts should be removed. Cysts can often be removed by electrocautery or cryotherapy. At the very least, sedation and a local anesthetic will be required, and many cats may need general anesthesia.
Warts and Papillomas
These growths are not nearly as common in cats as they are in people. They tend to occur on the skin of older cats. Some are on a stalk, while others look like a piece of chewing gum stuck to the skin.
Treatment: If they become irritated or start to bleed, they should be removed. In general, they are no threat to the health of the cat.
A lipoma is a growth made of mature fat cells surrounded by a fibrous capsule that sets it apart from the surrounding body fat. It can be recognized by a round, smooth appearance and soft, fatlike consistency. Lipomas grow slowly and may get to be several inches in diameter. They are not common in cats and are not painful.
Treatment: Surgical removal is indicated only for cosmetic reasons or to rule out a malignant growth.
A hematoma is a collection of blood beneath the skin, caused by a blow or a contusion. The area will be swollen, somewhat painful, and usually a reddish-purple color.
Treatment: Small hematomas may resolve spontaneously. Large ones may need to be opened and drained. Ear flap hematomas require special care.
A small knot may be present at the site of an injection and is often present for a few days in kittens who have been given their vaccinations. It seldom requires treatment. If a firm area remains where an injection was given or develops afterward, you need to contact your veterinarian immediately. This could be a vaccine-associated sarcoma.
A painful swelling beneath the skin may be an abscess. You can usually move and compress them, and they feel warm to the touch.