Tumorous growth affecting the skin of the horse. It does not affect any other organs. Various types are seen:
Verrucous: wart like growth in an on the skin
Nodular: firm, subcutaneous roundish nodules
Occult: circular patches of altered/thickened skin with thin haircoat, occasionaly with small nodules
Fibroblastic: fleshy, ulcerated and usually rapidly growing masses.

Horses of all ages can be affected and it can be extremely difficult to treat, as surgical removal is often followed by a recurrence. The exact cause is unknown although the Bovine Papillomavirus BPV is known to be involved in many cases. Particularly large tumors or an unfavourable location such as in the girth region can lead to loss of use of the horse.