What is a basal cell tumor?

A basal cell tumor is an abnormal growth/mass resulting from the uncontrolled division of basal cells. Basal cells make up the bottom (or basal) layer of the outermost layer of the skin, the epidermis. The epidermis lies above the dermis (which contains connective tissue, hair follicles, and sweat glands), and the hypodermis (made of fat and connective tissue). The basal layer is essentially the bottom and defensive layer of the epidermis. It contains many different types of cells, including those involved with inflammation.

Basal cell tumors are one of the most common skin tumors in dogs and cats. A basal cell carcinoma is a type of basal cell tumor that is malignant or cancerous. Less than 10% of basal cell tumors are malignant.

What causes these types of tumors?

The reason why a particular pet may develop this, or any tumor or cancer, is not straightforward. Very few tumors and cancers have a single known cause. Most seem to be caused by a complex mix of risk factors, some environmental and some genetic or hereditary. Certain breeds of dogs and cats are more likely to develop basal cell tumors, including Wirehaired Pointing Griffons, Kerry Blue and Wheaten Terriers, Cocker Spaniels, Poodles, and Siamese cats.

What are the signs of basal cell tumors?

Basal cell tumors vary in size (from 0.1 to 4 inches in diameter), and most commonly appear as a single, firm, hairless, raised mass in the skin, often on the head, neck, or shoulders. Occasionally they may be cystic or ulcerate, and some may stick out like stalks from the skin surface. The tumors are sometimes pigmented, especially in cats.

Although these tumors are not usually bothersome, if they develop in an area that can be scratched or chewed, there is the risk of self-trauma and infection. Your pet should not be allowed to scratch, bite, or lick these areas. Without surgery, these tumors may continue to grow and make surgical removal more difficult. For this reason, it is best to have your veterinarian evaluate any abnormal growths or bumps as soon as you notice them.

How are these types of tumors diagnosed?

Typically, these types of tumors can be diagnosed by a fine needle aspiration (FNA). FNA involves taking a small needle with a syringe and suctioning a sample of cells directly from the tumor 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 clear and biopsy may be necessary. A biopsy is a surgical excision of a piece of the tumor. Pieces of the tumor are then examined by a veterinary pathologist under the microscope. This is called histopathology. Histopathology is not only helpful to make a diagnosis but can indicate how the tumor is likely to behave.

How do these types of tumors typically progress?

Although these types of tumors are most often benign, meaning they are not cancerous and will not spread (metastasize) to the surrounding tissues or internal organs, without surgery tumors may continue to grow, with greater chances of ulceration, infection, and difficulties with removal. If the tumor is removed, the prognosis is excellent.

What are the treatments for this type of tumor?

Surgery is the treatment of choice for basal cell tumors and basal cell carcinomas. Surgery reduces the chance of secondary infection and inflammation as well, especially with tumors that are cystic or ulcerate. There are some reports of tumors recurring at surgical sites, but recurrence (regrowth at the same location) is rare. Cryosurgery, a technique that uses a liquid nitrogen spray to freeze the tumor, may be an option for treating smaller tumors.

Is there anything else I should know?

Your pet should not be allowed to bite, lick, or scratch the tumor, as this may cause it to ulcerate and bleed. As secondary infection is possible, your veterinarian may prescribe antibiotics if necessary.