Equine Disease Quarterly | EQUINE
There is compelling evidence that sarcoids are caused
by a bovine papillomavirus which is believed to be
transmitted by flies, most likely from infected cattle,
but possibly also from infected horses. It remains
unclear exactly how the virus leads to neoplastic
(cancerous) change, or why the virus is able to cause
disease in more than one species. Interestingly, a
(human) papillomavirus also is responsible for the vast
majority of cases of cervical cancer and an increasingly
large proportion of tumors of the head and neck in
humans; clearly there is much to be learned about the
implications of infection with papillomaviruses in all
species.
There is little doubt that there is a heritable component
to the disease. In warmbloods, the heritability has been
well demonstrated: Breeding two sarcoid-affected
horses vastly increases the risk of producing a horse
that develops sarcoids at some stage in its life. There
also appear to be breed-related differences in sarcoid
risk: Thoroughbreds are more likely to develop sarcoids
than Standardbreds, and Lipizzaners seem more
resistant to sarcoid development. Unlike melanomas,
there is no color predisposition and gender doesn’t
affect the chance of developing the disease. Specific
gene variations, noted in horses with sarcoids, are also
associated with virally induced cancers in humans. The
reasons for this association are unclear, but it is likely
due to differences in immune function and may explain
the apparent breed-specific variation in sarcoid risk.
Treatment options for sarcoids are numerous, with no
one option being suitable for every case. Traditionally,
sarcoids were often left without treatment, but as they
almost invariably become larger and more difficult
to treat, early intervention is strongly recommended
to avoid long-term sequelae. Treatment may involve
topical or intra-lesional chemotherapy or immune
modulators, surgical procedures, or radiotherapy.
Electrochemotherapy is a relatively new alternative
treatment option with apparently very good results, but
it unfortunately necessitates the use of multiple general
anaesthetics, so the risks must be carefully considered.
Appropriate treatment selection is largely dictated by
the location and type of the lesion (Figure 2). Laser
surgical excision is the author’s treatment of choice for
the majority of lesions in locations other than around the
eye; periocular lesions are treated via radiotherapy with
great success. Reported success rates for laser surgical
excision are in the order of 83% and for radiotherapy
are around 90%; compared to other treatment options
they represent the least risk to the horse and lead to the
best results. However, not every lesion—or horse—is a
suitable candidate for these treatments, and the key is
to select the method most likely to be successful in the
first instance. Recurrent sarcoids become increasingly
difficult to manage and convey a far worse prognosis
than those appropriately treated in the first place.
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After treatment
• Volume 21 Issue 2 | May 2019 •
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