May
27
Written by:
Surgi-Care Center for Horses
5/27/2011 5:12 PM
Sarcoids
are a benign form of tumor found on the skin of horses. They are commonly associated
with bovine papillomavirus, which causes warts in cattle. There is some evidence
to suggest that flies play a role in their transmission to horses. Quarter Horses
are more susceptible than other horses but all breeds, ages, and genders of horses
are at risk of developing sarcoids. There is also some evidence of genetic
predisposition to development of sarcoids.
Sarcoids
most commonly develop on the legs, head, and underside of the neck or belly, but
can occur anywhere on a horse’s body. They also frequently appear in areas of scarring,
or wound sites. They are categorized by their appearance. Different types of sarcoid
tend to exhibit different growth rates, and some are more locally aggressive
than others.
Occult
sarcoids are fairly flat hairless areas, which are often roughly
circular. They may have some thickened skin and occasionally have nodules in
them. Occult sarcoids tend to grow slowly. They may develop into verrucous
sarcoids, or if injured, may develop rapidly into the fibroblastic form.
Verrucous
(warty) sarcoids look like clusters of warts with scaly thickened skin. They can
vary in size from less than a dime to fairly large, extensive lesions. A flat
area of thickened, hairless skin often surrounds them. Like the occult
sarcoids, these tend to be slow growing, but may become aggressive if injured.
Nodular
sarcoids develop underneath the skin surface. They are spherical tumors,
with greatly varying sizes. The skin covering them appears normal, but can
become thin. If the skin becomes damaged, these can also quickly develop into
fibroblastic sarcoids.
Fibroblastic
sarcoids look like proud flesh. The tissue appears “raw” and will often have
a clear yellow discharge. Any of the aforementioned tumors can develop into
this type if they are injured. Fibroblastic sarcoids also tend to appear at
wound or surgical incision sites. These tumors tend to be more rapid growing,
and more invasive of the local tissues. They do not metastasize, however.
Mixed sarcoids contain
components of the occult, verrucous, and fibroblastic types.
Malevolent
sarcoids tend to develop from other types of sarcoid that have been repeatedly
injured, or had multiple attempts at surgical removal. Some malevolent sarcoids
develop spontaneously, however. This type can be very aggressive and spread along
tissue planes or through cords of lymphatics.
Diagnosis
of equine sarcoid is commonly made by their physical appearance. Biopsy will
frequently allow for definitive diagnosis, but injury to the tissue frequently
leads to development of a more aggressive type of tumor. If biopsy is
attempted, it generally involves removal and submission of the entire tumor.
Unfortunately, it is often difficult to determine the underlying extent of the
tumor, so recurrence is common in surgically excised sarcoids. Consult your
veterinarian for diagnostic options if you suspect your horse has sarcoids.
Due to
the high incidence of recurrence, and the tendency for sarcoids to transform into
a more aggressive form after injury, the slow growing types of sarcoid are
frequently best left alone. They should be monitored closely for evidence of
transformation into a more aggressive type of tumor. If your horse has a
sarcoid that has a sudden increase in growth rate, or a sudden change in
appearance, you should contact your veterinarian as soon as possible.
Surgical
treatment options include ligation (for nodular sarcoids), surgical removal, cryosurgery
(freezing the tumor with liquid nitrogen), hyperthermia (treatment with heat), electrocautery,
and laser surgery, or any combination of the above. The last four methods on
the list generally require multiple treatments. No one treatment is 100%
successful and recurrence is common, as is development into a more aggressive
tumor.
Medical
options include topical applications of chemotherapeutic agents such as 5 FU, intralesional
injection of chemotherapeutic agents such as cisplatin, radiation therapy, or topical
treatment using immunotherapy such as BCG or XXTERRA. Success rates with some
of the above medical therapies have been quite encouraging, however all of
these treatment modalities can have unwanted side effects. Many of the
treatments can be quite expensive. Discuss treatment options thoroughly with
your veterinarian so that she or he can help you make the best decision for you
and your horse.
Contact
Surgi-Care Center for Horses at 813-643-7177 or email lkuebelbeck@surgi-carecenter.com with
any questions regarding this topic.