Page 6 - Clinical Connections - Summer 2022

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