Sarcoids are the most common tumor in Equidae (horses, mules, and donkey). Sarcoids are locally aggressive, fibroblastic tumors of the dermis and subcutaneous tissues that are thought to be associated with bovine papillomavirus infection.
Different clinical manifestations include occult, verrucous and nodular or fibroblastic types.
Multiple lesions in the same horse with typical sarcoid morphology
(Aggressive) recurrence after treatment
Therapies include surgical resection, interstitial radiation, intralesional chemotherapy, and nonspecific immunotherapy.
The main types are sarcoids are:
**Verrucose **– These are slow growing and have flat, scaly tumours and look like scars or ringworm. They are the least aggressive sarcoid type.
**Nodular **– These are well demarcated lumps, which may be covered by normal skin or may be ulcerated. They have a spherical appearance and may have a wide, flat base or narrow stem-like base. They have a medium growth rate and their behaviour may change over time.
**Fibroblastic **– These are aggressive tumours that grow rapidly and are locally invasive, possibly invading down into the tissues underneath the skin. They might not be well demarcated and often occur in clusters of tumours of variable size and shape. They have an irregular appearance and because they grow rapidly are often ulcerated.
Mixed sarcoids are combinations of the above three types and it is fairly common for horses to develop multiple sarcoid types in one region or for there to be multiple sarcoid types present at different sites around the horse.
Occasionally horses develop malignant sarcoids which are highly aggressive and spread locally via lymph vessels producing lines of sarcoids spreading from the original tumour site.
Therapies
Medical treatments include the immune stimulant Bacillus Calmette Guerin (BCG) vaccine (which is used to prevent tuberculosis) injected into the tumour; the injectable chemotherapy drugs cisplatin and Mitomycin C which act by interfering with DNA copying in tumour cells; the topical chemotherapy cream AW4-LUDES (‘Liverpool cream’); ointments containing extracts of the blood root plant, and various other natural remedies. Other treatment continue to be translated from human medicine including photodynamic treatment in which a chemical is applied to the surface of the tumour and then exposed to a specific type of light which activates the chemical and kills tumour cells.
Electrochemotherapy (ECT)
Surgical treatments include surgical excision, cryosurgery (freezing) and laser surgery.