ADVICEFROMTHE VET EQUINE TUMOURS By Emily F. Floyd BVSc, DipACVIM, MRCVS


Thereislimited oncology research available in equine medicine,possibly because diagnosis canbechallenging and expensive, with clinical signs of tumours often being non-specific, requiring referral to veterinary specialists. Early detection of internal tumoursis


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essential when considering the likelihood of successful treatment. Your vetmay suspecta tumour when other differential diagnoseshave been ruled out, or when the horse doesnot respond to therapeutic measures. Some tumoursare thought to be caused by


viruses, while exposuretosunlight (ultraviolet) mayprovoke skin tumoursinunprotected areasofthe horse,and on light-coloured horses. Anytype of growth should be seen by your vetassoon as it is discovered. Some of the morecommon typesofequine tumour areoutlined below.


SARCOIDS Sarcoids arethe mostcommon form of equine skin tumour and arelocally invasivetumours that do not spreadtoother areasofthe body. Different typesofsarcoid existwith differences in sizeand appearanceand usually occur in thin skinned areasofthe horse,such as the girth area,sheath, inner thigh, around the eyes and in the ear. There is agenetic predisposition to disease susceptibilityand breeding from ahorse with ahistory of sarcoids is likely to produceahorse that suffersfromsarcoids. Sarcoid lesions canbeslowgrowing or


remain static forlong periods of time.Most commonly,however,theywill grow larger at their original siteand multiply in number.They canbecome painful and thereforeawelfare issue,particularly around the eyes.Following clinical assessment, your vetwill advise the mostappropriatetreatment options. Treatment is often difficult and invasiveand


thereisnosingle entirely reliable therapyfor the elimination of all typesofsarcoids. Surgery is an option, but failuretoremove


the sarcoid in full mayresult in the recurrence ofamoreaggressivesarcoid. Laser surgery canbeeffective forsome typesofsarcoids (typically those around the groin and sheath area)and cansometimesbeperformed on standing,sedated horsesusing local anaesthesia. Astudy at RossdalesEquine Hospital involving 73 horseswith 290 sarcoids showedahigh rate of success. ‘Liverpool sarcoid cream’ is atopical chemotherapytreatment which canonlybe obtained by veterinary prescription and should only be applied by avet. Sarcoids usually


Fig1Laser surgery to remove asarcoid beingcarried out under standing sedation and local anaesthesia


look alot worsebeforetheyimprove as theybecome swollen and inflamed, which maybepainful to the horse. Radiotherapyisavailable fortreatment of sarcoids


and other tumours. Brachytherapyinvolves high dose radiation being administeredtostanding, sedated horsesfor the treatment of peri-ocular sarcoids and resultstodatehavebeen very good. Electrochemotherapy, which involves injecting a chemotherapydrug intothe sarcoid and then applying an electric current that drives the drug intothe sarcoid cells, has recently been trialled and shown to be useful in some cases. This type of treatment mustbe performed under general anaesthesia and often needs to be repeated at alater date.


MELANOMAS


Melanomas aretumoursofpigment cells, predominantly seen in older,greyhorses, but theycan be found in horsesofany colour or age.These tumoursare usually slowgrowing and often develop under the tail, in the groin region, in and around the eyes,and in the parotid salivary glands. Although mostequine melanomas areusually


benign, theycan occasionally become malignant. Those that occur in non-grey horsesare often morelikely to cause problems. Early removalof some tumoursmay prevent development into malignant cancerous growths. However,whilst melanomasmay look unpleasant, some horses mayhavethese formanyyears without clinical problems. Other melanomas, such as parotid melanomas, maygrowsolarge that the horse is unable to eatordrink properly, flex itspoll or turn itsheadfromside to side. Veterinary advice should be sought to confirm diagnosis. Treatment is often by surgical or laser removal.


Intralesional chemotherapycan sometimesbe used with drugs injecteddirectly intothe tumour tissue.A vaccine(Oncept) canbeused to treat melanomas in some horses, but thereislimited information about itseffectiveness.


SQUAMOUS CELL CARCINOMA (SCC)


Fig2Peri-ocular sarcoidscan be treatedwithbrachytherapy (radiotherapytreatment)


Squamous cell carcinoma (SCC)isaninvasive, aggressivetumour that canaffectvarious skin structures,mostnotably the eyelids,towards the inner eye, the mouth and penile skin in male


quine tumours cantakea number of forms and the causesofdevelopment are not alwaysfully understood.


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FEBRUARY/MARCH2021


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