Conditions or ailments that are the cause of a problem that you see - your observation.

Your vet may diagnose

Squamous Cell Carcinoma of Sheath or Penis


Squamous cell carcinoma is a common cancer (tumor) of the sheath and penis in middle-aged and older horses. Other tumors can appear in this area, but they are far less common.

Squamous cell carcinoma appears as variably sized raised pink to red, warty to ulcerated areas on pink skin. It varies from slow to rapid growing. Each cancer is specific in terms of its aggression (malignancy).

This condition is is far more common on unpigmented skin of the sheath and penis. It is also much more common in horses living at high altitudes, in arid regions with intense UV light.

I practice in New Mexico at 2130 meters (7000 feet) elevation, and this condition is very common here. American Paints and Appaloosas are the breeds commonly affected. I have also seen this condition in Belgians, Pintos, Appaloosas, and individual Palominos.


Vets make presumptive diagnoses of this condition frequently, based on location and appearance of a growth on pink skin. Biopsy and microscopic examination by a pathologist may yield additional information that is helpful in recommending treatment options.

my vet's role


Prognosis depends on age, size, location and characteristics of the mass, and biopsy results. Recurrence in the same place or other places is common. Prognosis is fair good if diagnosed and treated early.

my role


I might observe

You might make these observations when a horse has this condition.

Very Common
Less Common
more observations

Questions To Ask Your Vet:
  • What should I do to monitor my horses for this condition?
  • What is the likelihood of successful treatment?
  • What is the next step if this treatment does not work?

Look for signs of this disease in horses with pink skin, and older horses. Inspect this area prior to purchase of a new horse, keeping in mind how common this condition is. Have a vet perform a prepurchase exam, looking for this condition.

Inspect your horse's penis on a regular basis, which you can do for many horses while they are urinating. Routine veterinary inspection of this area is also important, and can be combined with a sheath cleaning during semi annual routine healthcare visits. Vets often tranquilize horses before cleaning their sheath to relax the penis, which makes cleaning and visual inspection of this area easier.

Author: Doug Thal DVM Dipl. ABVP