Could laser excision be a more effective option for the removal of troublesome sarcoids? Philip Ivens MRCVS discusses the latest thinking

Sarcoids are the most common skin cancer affecting equines. These tumours originate from cells called fibroblasts, which play a critical role in wound healing by producing the extracellular matrix and structural proteins that bind the body together.

Fibroblasts also produce scar tissue, which is one of the reasons that sarcoids can be so difficult to treat. Most treatments stimulate scar tissue — which exacerbates the problem.

The site of these locally invasive fibroblastic cancer lesions can be troublesome, especially if growths appear in the girth area, groin, in the ear or around the eye. Sarcoids are very likely to recur. They can become more aggressive if subjected to accidental or deliberate interference, such as rubbing by tack or failed treatment attempts.

The virus connection

Historically, young horses — between 1 and 6 years old — and geldings were thought to be more predisposed to sarcoids. Recent evidence suggests that there is actually no significant breed, sex or age predisposition.

We have long known that there is a genetic element to the condition, and that horses related to sarcoid-prone animals are more likely to develop the problem themselves. This genetic predisposition is not a simple one, however. It is most probably polygenetic — influenced by more than 1 gene — and further affected by a complex interplay of environmental factors, such as exposure to skin trauma in the form of wounds or rubbing.

At the moment, we are not in a position to categorically advise whether or not horses affected by sarcoids should be used for breeding, as it’s likely that genetic predisposition probably exists in a far higher number of horses than those who show the disease. Careful consideration of breeding lines with a high incidence of sarcoids should be undertaken.

The shift in our understanding of equine sarcoids in recent times concerns the role of a virus. Viruses and cancers have had a long association — Marek’s disease in poultry, discovered at the beginning of the 20th century, is an early example. More recently, some types of human papillomavirus (HPV) have been found to increase the risk of cervical cancer in humans.

Bovine papillomavirus (BPV) types 1 and 2 are causally associated with the development of equine sarcoids. We are in the early stages of understanding BPV involvement with horses, but we do know that a horse with the virus will not necessarily develop sarcoids.

Genetic and external environmental factors must also come into play. BPV has been found in biting flies and it is a reasonable hypothesis at this time that biting insects can transfer the virus. This may well account for the distribution of sarcoids commonly seen in areas favoured by such insects — around the head, the “armpits”, underneath the belly and in the groin and sheath area.

To treat — or not?

Isolate sarcoid lesions can be slow growing or remain completely static for years. Rarely, they regress spontaneously as the body mounts an appropriate immune response.

Understanding how this occurs is key to the development of future treatment. Most commonly, however, sarcoids will grow larger at their original site or multiply in number. They can transform randomly from a benign-looking nodule to an ulcerated fibroblastic lesion.

The course of this condition is entirely unpredictable. It is therefore wise to consider every lesion with the respect skin cancer deserves, monitoring it closely for progression and considering possible treatment. Future research may allow us to quantify a particular horse’s genetic predisposition and risk profile.

Until then, removing the lesions early seems prudent, given the recent advancement in our knowledge of the involvement of BPV and the potential for flies to transmit the virus.

Success rates are improved by early intervention. Whether — and how — to treat a sarcoid remains a veterinary challenge. Intervention can encourage the “seeding” of tumour cells and incite fibroblastic transformation, bringing about a high chance of recurrence. Many sarcoids are sited in difficult or delicate anatomical areas. Treatment can be costly, involving time out of ridden work, and possible complications include scar tissue formation.

There are many treatment options and my preference would be for an integrated multimodal approach. One treatment is, sadly, not universally superior to others. Tumour position, type, previous treatment history, patient temperament and athletic use or demands are all important considerations. Often a combination of techniques will need to be employed in more complicated cases. Experimental treatments without proper scientific analysis and supervision, such as nonprescribed creams such as toothpaste, can make sarcoids transform into more aggressive forms. Veterinary involvement is highly recommended.

What is laser removal?

A laser is a specialised piece of surgical equipment that cuts and vaporises tissue, with minimal bleeding, to kill any potential cancerous cells. Laser treatment also allows easier visualisation of the tissue to be removed. The sarcoid can be removed under standing sedation and local anaesthetic, or under general anaesthetic.

Depending on its anatomical location and nature, as much of the normal tissue (or margin) as possible is taken along with the tumour. The underlying area, referred to as the surgical bed, is then marked with a crosshatch pattern with the laser to vaporise any remaining potential cancerous cells.

The patient receives anti-inflammatories and antibiotics before and after the surgery. Personally, I then prefer to leave the surgical site to heal by itself from the inside out. The site will usually form a large scab from the laser within 5 to 7 days, which will slough off over time, leaving healthy healing tissue known as a granulation bed. The extent and location of surgery will dictate the healing rate, but everything has usually resolved within 4 to 6 weeks.

Depending on the time of year, insect repellents and protective creams may be needed. It’s possible that ridden work can be resumed before this time, depending on the size and site of the healing wound. Few of us can control the genetics of our horses, so it seems sensible in most cases to remove the source of the BPV from the flies to try to prevent the spread of sarcoids to elsewhere on the horse. Laser excision is a valuable tool to this end.

Laser excision: pros and cons

✓ Healing times are relatively rapid, especially if the sarcoid is tackled when small — meaning less time out of work

✓ Cosmetic results are often very good

✓ Can be effective in difficult anatomical areas, such as the ears

✓ Minimal complications

✓ Success rates can be high — as indicated by research last year [2013] at Rossdales equine hospital involving 73 horses with 290 sarcoids

✗ May not be suitable in all cases, such as deeprooted sarcoids or those in difficult anatomic areas lacking a sufficient margin of normal tissue

✗ Surgical time can be lengthy, as the laser does not cut quickly — patience and experience are required

✗ Specialised equipment and time can make the cost prohibitive, although this has come down in recent years. Start-to-finish costs are comparable to many other treatments and the procedure is becoming more widely available

Know the enemy

Your at-a-glance guide to sarcoids:

Occult: a hairless patch with either small nodules or a roughened, thickened area of skin

Verracous: a scaling, warty appearance with variable degrees of flaking; can be on a stalk

Nodular: can be within the skin or lying underneath it; as it enlarges, the skin over the nodule can ulcerate

Fibroblastic: a fleshy appearance that can have a narrow stalk or a broad attachment

Mixed combinations of different types: these may change with time

Malignant/malevolent: a rapidly aggressive and highly invasive form

Picture by Philip Ivens