By Dr. Ashley Schofield
Sarcoids are a type of skin tumour in horses, they are caused by the bovine papilloma virus. They are persistent and frequently progress with time. There are some sites that seem to be more commonly affected such as the face, axilla and groin. Whilst it is theorised that these regions correspond to common areas of fly activity only parts of the virus have been found in flies. Sarcoids are generally non-itchy and non-painful. They can be categorised based on appearance:
Verrucose – Flat, warty and scaly appearance
Nodular – These are well demarcated lumps, which may be covered by normal skin or may be ulcerated.
Occult – Roughly circular hairless areas, subtle.
Fibroblastic – Locally invasive, possibly invading down into the tissues underneath the skin. They might not be well demarcated and often occur in clusters of tumours of variable size and shape.
Mixed sarcoids are combinations of the above three types and it is fairly common for horses to develop multiple sarcoid types in one region or for there to be multiple sarcoid types present at different sites around the horse.
Occasionally horses develop malignant sarcoids which are highly aggressive and spread locally via lymph vessels producing lines of sarcoids spreading from the original tumour site, these generally carry a poor prognosis and are challenging to treat.
Diagnosis: Sarcoids are commonly diagnosed by appearance and it is generally not recommended to biopsy part of a sarcoid as this can make them more aggressive. Biopsy results can be obtained if the sarcoid is removed surgically.
Treatment of sarcoids will vary greatly dependent on the type, finances, severity of disease, location of sarcoid and many other factors. I will briefly go through a few of the most common ones but by no means are these the only ones.
Surgical removal: Usually done with a surgical laser (Ideally CO2 laser) and usually sending the sarcoid off for histopathology to assess surgical margins. Laser is preferential over simple scalpel blade excision – which is not commonly performed due to laser giving a better prognosis. Surgical removal can be done with local anaesthetic and standing sedation in most cases, though some cases may require a general anaesthetic.
Chemotherapy creams: These can be applied post-surgery or as a sole therapy. These creams usually requires a vet to apply the creams as they are very potent. They are applied in certain intervals following a protocol, these creams are designed to kill off the cells and over days/weeks/months dependent on sarcoid type/location/case the lesion will die off and eventually will slough off.
Intralesional injections: This is when chemicals (usually chemotherapeutic) are injected directly into the lesion to kill off the sarcoid.
Banding: This is when a tight band (usually lamb castration kit) is applied to the base pf the sarcoid to cut off blood supply to the sarcoid to kill it via preventing oxygen and nutrients. This can only be performed on appropriate sarcoid types.
Electrochemotherapy: Relatively new therapy and can be combined with surgical or chemotherapy treatment and is having brilliant results. However, this does require a brief general anaesthetic.
Treatment summary: There are lots of different options. The practice I work for use a skin specialist and the current thoughts are that CO2 laser excision is the gold standard giving the best prognosis – this will of course be surgeon dependent. There are LOTS of other therapies than above, but listing them all would be extensive.
A small number of horses seem to be able to spontaneously recover from sarcids however the percentage of horses with sarcoids that do this has been estimated at 0.1% – therefore not to be relied on. Although fly transmission has not been proven it is often advised that fly control can be beneficial in prevention.
Other skin tumours:
Frequently seen in grey horses and appear as dark grey/black nodules in the skin. Unlike sarcoids melanomas are more likely to develop internally. They become more common after 10 years of age and commonly affect the head, neck and underside of the tail (perineal region). They are not limited to the skin and can occur anywhere in the horse, such as salivary glands, guttural pouches, gastro-intestinal tract to name a few. It is possible for melanomas to cause serious and severe disease where they become truly cancerous and cause multiple issues internally dependent on the organs and extent of disease.In some cases the melanomas (especially those under the tail) can become ulcerative.
Treatment of melanomas varies dependent on the location, however if skin based then surgery is the most common therapy currently used though may not be easily performed if severe case. A melanoma vaccine is available but more time is needed to get data on the efficacy of this in horses. Other therapies are available such as intra-lesional injections and chemotherapy.
SQUAMOUS CELL CARCINOMAS
They are commonly found on the skin but can affect other tissues. If effecting the skin they are more commonly around eyes, vulva or the penis especially those individuals with pink skin (e.g. appaloosas). They are able to spread to internal organs but usually first spread to a local lymph node before doing so. They usually look like small sores or bumps, they are often easy to spot around the eyes but become more difficult to spot around the genitals. Other tissues and organs affected will show varying clinical signs dependent on location.
Treatment of SCCs can be complex and is not always possible dependent on location. SCCs affecting the skin are usually surgically excised with a good margin and then sent off to a lab to ensure margins are complete and aggressiveness assessed. Chemotherapy and radiation are other possible treatment options (more commonly used for internal SCCs). Intra-lesional injections can also be used in some cases. UV light can have a factor in causing SCCs and so pink skinned horses should be provided with extra protection.
What is a biopsy?
A biopsy aims at looking at a sample of tissue under a microscope after correct preparation. Commonly in skin tumours the entire lesion is surgically removed and the entire lesion is sent to the lab. The lab then evaluate and identify the type of tumour based on the cell population but also look at the perimeter of the sample and check that the margins have healthy skin to ensure the tumour was removed entirely. Biopsies can also be part of the lesion, where a small sample is removed and the lab evaluate and identify the cell type, based on the results treatment is decided.
Biopsies are not always conclusive (especially when small samples are taken) and so may need to be repeated. Biopsies are not only performed on skin tumours, other skin cases may warrant a biopsy as can other diseases of other organs (e.g. liver disease).
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