Sarcoids, benign skin tumors which often form at wound sites, are quite common but they are easily confused with other tumors, diseases and lesions. The chief cause of confusion stems from the fact that sarcoids have such varied appearances: flat, knobby, wartlike or ulcerated. A biopsy-removal of a bit of tissue for microscopic examination of its cells-is the only sure way to determine whether a growth is a sarcoid or one of the following conditions.

Proud flesh: Ulcerated or mixed sarcoids have a thin layer of granulation tissue that can look like proud flesh, also called exuberant granulation. Proud flesh, like sarcoids, is often treated with excision.

Keloids: These hard, raised lesions are a form of mature granulation tissue that infiltrates fibrous tissue. They can look like verrucous or mixed sarcoids. Keloids occur on the limbs, especially in wounds that have not received care. Chemotherapy, cryosurgery and radiation are possible treatments.

Ringworm: This fungal condition can look a lot like flat sarcoids, producing flat, slightly thickened, generally hairless, round or oval lesions. Ringworm, perpetuated in warm, damp, poorly ventilated stables, is treated with topical antifungal agents.

Viral papillomatosis: Also called warts, viral papillomatosis shares characteristics with verrucous sarcoids. Warts are usually found on horses younger than 3 years old. The lesions are small-usually no bigger than three-quarters of an inch-and often cluster around the muzzle, but they can be found anywhere on the head. As young horses develop natural immunity, the warts disappear on their own within a few months.

Squamous-cell carcinoma: Closely resembling ulcerated sarcoids, these malignant tumors are caused by chronic sun exposure. They are found primarily in lightly pigmented horses and result when ultraviolet light causes malignant changes in the cells. Squamous-cell carcinomas commonly appear on the head, genitalia and under the tail but are not limited to those areas. They are treated by excision, cryosurgery, chemotherapy and radiation therapy.

Fibroma/fibrosarcoma: Fibromas and the more aggressive malignant form called fibrosarcoma resemble large knots covered by normal skin, but they can rupture and become ulcerated. Their cause is unknown, and they tend to occur around the eyes. Depending on the stage of development, sarcoids and fibroma can be very difficult to differentiate, even with a biopsy. Treatment consists of surgical excision followed by laser or radiation therapy. Incomplete removal can lead to recurrence of more aggressive tumors.

Lymphosarcoma: Consisting of intact hair and skin overlying lumps beneath the skin, these growths can occur anywhere on the body and in multiple locations. Possibly of viral origin, they respond best to surgical excision rather than chemotherapy or cryosurgery.

Melanoma: Benign or malignant tumors, melanomas are slow-developing growths that form under the skin, commonly around the ears and heads of gray horses. They can be round and nodular or ulcerated. When possible, melanomas are excised and biopsied. Unlike other growths that consist of reddish-pink tissue, melanomas are usually black inside.

This article originally appeared in EQUUS in May 2001.