Page 6 - Clinical Connections - Summer 2022

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Page 6 - Clinical Connections - Summer 2022
P. 6

RVC RESEARCH    STUDY    VETERINARY SERVICES       RVC.AC.UK
         Equine

        TARGETED MELANOMA TREATMENT FOR
        INOPERABLE AREAS OF HORSES



          n  January  the  RVC  Equine  Referral   into tumour cells.  The equipment is safe,   The RVC appears to be the only
          Hospital began to offer a novel treatment   easy to use and can be performed in   equine service in the UK currently using
        I for equine melanoma using locoregional   standing horses without the need for a   this  technology  to  treat  melanoma.  The
        hyperthermia combined with intratumoral   general anaesthetic.          Thermofield  unit  was  funded  by  the
        chemotherapy.  The  treatment  specifically   Though it  is not expected to result   RVC Animal  Care  Trust. Hyperthermia
        targets  tumours  that  cannot  be  surgically   in  complete  remission,  locoregional  and  chemotherapy  have  been  used  in
        removed,  thus  enhancing  the  service  that   hyperthermia  and  intratumoral  human oncology for many years, and the
        RVC  equine  specialists  can  offer  and   chemotherapy is aimed at tumour shrinkage,   combination has been reported to result in
        improving the quality of life for horses   thus improving function and quality of life in   a reduction in tumour size and improved
        affected by this disease.           affected  horses.  In  many  cases  treatment   survival rates for a variety of cancers. There
          Melanoma is a very common nodular   will be performed in concert with diode laser   is currently no published data on the efficacy
        skin disease that affects older grey horses   removal of other tumours that are amenable   of this multidisciplinary treatment for equine
        of any breed. The disease is caused by a   to surgical removal. Prior to embarking on   melanoma, however, results from preclinical
        single gene mutation that increases the   treatment, the horse will be examined, and   studies have been promising.
        activity of melanoblasts. This manifests as   an individually tailored treatment plan will be
        a grey coat colour, however over time it   devised based upon the size and location of
        also results in malignant transformation of   the tumours.
        these cells, leading to the development of   Horses that meet the criteria receive three
        melanocytic tumours. This gene has been   rounds of treatment, with a week between
        bred into horses over millennia, as the grey   each.  Treatment involves  injection  of  the
        horse was venerated by ancient cultures,   cytotoxic drug into the melanoma, followed
        and consequently it is estimated that up to   by  locoregional hyperthermia using the
        80 per cent of grey horses over the age of   Thermofield system that utilises microwave
        15  years  will  develop  melanoma  at  some   energy to heat the tissues. The procedure
        point in their lifetime.            takes about an hour to complete. A second   Application of the Thermofield heat pad for a
                                            hyperthermia  treatment  is  performed  the   patient called Murphy
        Targeting and effectiveness         following day and the horse is discharged
        Though several treatments are available for   until the second and the third treatment   Discussing  the  development  and
        equine melanoma, none are 100% effective   rounds. The treatment is not associated with   ramifications for patients and their owners,
        – and some lesions are not amenable   any side effects and is well tolerated by the   Dr Michael Hewetson, Senior Lecturer in
        for surgical removal. For example,   horse.                             Equine Medicine at the RVC, said: “Although
        melanomas affecting the parotid region                                  locoregional  hyperthermia  combined  with
        and other anatomically sensitive areas.                                 intratumoral chemotherapy is a relatively
        Locoregional hyperthermia combined                                      new treatment in equine oncology, I have
        with intratumoral chemotherapy has been                                 been impressed with the response in the
        specifically developed to target these                                  horses that we have treated thus far, and
        tumours. Hyperthermia transfers a large                                 I am optimistic for the future. We will be
        volume of electromagnetic energy deep                                   collecting data over the next few years to
        into the patient’s tissue. The absorbed                                 report on its effectiveness.”
        energy causes molecular friction, heating
        the targeted area to the febrile range (41 -
        42⁰C) that has been shown to have a direct
        killing effect on tumour cells. This is likely
        due to heat shock induced apoptosis and
        alterations to the structure of proteins that
        support DNA metabolism, thus inhibiting
        repair of damaged tumour cells.
          Additional mechanisms that may play
        a role include direct damage to tumour
        vasculature  and  production  of  heat  shock
        proteins that stimulate an innate and   Application of locoregional hyperthermia   The thermofield unit's monitor
        adaptive  immune  response  to  the  tumour.     with the Thermofield heat pad following
        Importantly, hyperthermia has also been   intratumoral injections of cisplatin. This horse
        shown  to  have  a  synergistic  effect  with   had multiple confluent perianal melanomas     For equine referrals, please call: 01707
                                             under the tail and significant tumour
        various cytotoxic drugs (e.g. cisplatin or   shrinkage was seen following treatment  666297
        carboplatin) by increasing drug penetration                                    Email:
                                                                                     equinehospital@rvc.ac.uk

        6   Summer 2022
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