Fortunately, cancer is not as common in horses as in humans and some other animal species. Tumors of the skin are the most prevalent type of neoplasia (cancer) seen in equines. Although they may look harmless at first, sometimes skin masses can grow and spread out of control if they are ignored.
Ideally, skin tumors should be removed when very small and submitted for analysis. This is called excisional biopsy.
Three types of skin tumor are most common in horses:

Squamous cell carcinoma usually occurs on the face and perianal/preputial areas, commonly in horses with non-pigmented (white) skin (Appaloosas, Paints, Pintos), although the tumor does not necessarily affect only white skin.

Melanoma usually occurs in gray horses with heavily pigmented (black) skin in the perianal area and tail base, also can occur in the parotid (throatlatch) area and guttural pouch. Melanoma can occur in horses of other colors, and is usually a more aggressive tumor in non-gray horses.

Sarcoid can occur anywhere on the body but usually found on the face, thorax or legs. The sarcoid can come in several types: flat (a thickened area with no hair), verrucuous (warty appearance), or fibroblastic (looks like a wound with proud flesh).

If your horse develops a growth on or under the skin, have your veterinarian examine your horse as soon as possible. He or she will decide whether to perform a biopsy or remove the tumor and then submit it for analysis. Therapy to remove tumors is always more successful if performed early in the course of disease!

Treament for Skin Tumors

Complete surgical removal:
The first line of defense for skin tumors. In order to achieve complete removal of a tumor, at least a 1 cm (3/4 inch) margin of healthy tissue must be removed on all sides of the tumor. Consequently, if the tumor is allowed to get very big, a large amount of tissue must be taken out in order to try to prevent re-growth of the tumor. In some areas such as near the eye or on the lower leg, lack of loose skin or proximity to vital structures can make complete removal almost impossible. Even when adequate healthy tissue is removed with the tumor, sometimes tumor cells can be left behind. This is especially common with sarcoid tumors. These tumors send out invisible strands of neoplastic cells that allow for spread and regrowth of the tumor. Surgical removal can be performed in the traditional manner with a scalpel, or, by using a surgical laser. Willamette Valley Equine is fully equipped to perform laser surgery. Lasers work by using a focused beam of light energy to cut tissue and coagulate (clot) vessels. In addition, the thermal energy can be used to heat the surgical area to a temperature that will also help kill any remaining tumor cells. This helps prevent tumors from reoccurring after they are removed.

Cryotherapy:
Liquid nitrogen is used to freeze small tumors or a tumor bed after surgical removal. This is another method to kill any remaining tumor cells left after tumor removal. This therapy is also available at Willamette Valley Equine.

Chemotherapy:
Anti tumor drugs such as Cisplatin can be injected around small tumors or tumor beds after surgical removal of the mass. This treatment is very valuable for treating tumors around the eye or when tumors cannot be completely removed. This treatment is also available at Willamette Valley Equine.

Radiation Therapy:
This modality can be very effective for invasive tumors that cannot be completely removed. The horse must be anesthetized for the procedure. This treatment is only available at select universities.

Always have your veterinarian visit and examine your foal within the first 24 hours of life. He or she will examine your mare and foal and decide if any tests or treatments are necessary. Unfortunately, the problems described here are only a few of the problems that can affect the newborn foal. Early detection and prevention of the problems make for happy, healthy foals!