Andy Fiske-Jackson, Deputy Head of RVC Equine and Associate Professor in Equine Surgery

RVC Equine has long been at the forefront of furthering equine oncology, with the use of novel chemotherapeutic drugs and multi-modal treatment regimes. This includes a range of treatment modalities for sarcoids, tailored to the specific needs of individual patients.

Modalities we use for treating sarcoids at RVC’s Equine Referral Hospital include electrochemotherapy (ECT), tumour specific electroporation (TSE) and thermofield treatment.

We have been offering ECT to treat sarcoids since 2017. RVC Equine was the first veterinary centre in the UK to offer that treatment option. This treatment involves injecting carboplatin, followed by application of a small electric current across the sarcoid.

The procedure can be combined with other sarcoid treatments, such as laser excision. ECT is especially valuable for sarcoids in areas where cytotoxic cream cannot be safely applied, such as around the eye, or where the cream could be rubbed onto unaffected areas.

Three ECT treatments are usually required, all under a brief general anaesthetic or standing sedation, if the treated area can be desensitised with nerve blocks. Larger sarcoids may require surgical debulking beforehand.

ECT has been shown to be quick, safe and efficacious but other treatment modalities are more appropriate for certain sarcoids.

Tumour Specific Electroporation

Since the end of 2022 we have also been able to offer TSE treatment. This modality compared to others is especially useful for the treatment of large tumours and sarcoids situated over vital structures, such as joints, large blood vessels or the parotid region. Surgical resection and topical cytotoxic creams carry a large risk of damage to these vital structures.

The cytotoxic drugs available for use in horses work by preventing cell division. However, the uptake of these drugs into the cell is very limited due to the intact membrane of the target cancer cell. Applying an electric current to the cell causes pores to open in the cell membrane, allowing the drug to enter the cell.

Bleomycin, the drug we use with TSE, is increased in its concentration in the cell by several hundred-fold or more following application of an electric current. This process is called electroporation. This concept had already been adopted by ECT machines.

We have enjoyed good success with treating small shallow sarcoids in horses with ECT but static ECT can cause unwanted thermal necrosis and destruction of normal tissue. TSE is an innovative dynamic electroporation, designed to avoid such unwanted destruction of the surrounding normal tissue by constantly measuring the conductivity of the tissue and adjusting the pulse train accordingly. TSE also stimulates the host immune system to attack the tumour or sarcoid.

Like all machines and technologies, we are continuing to learn how to optimise the use of TSE. We have found the procedure does require a general anaesthetic unless we can desensitise the area to perform the treatment under sedation, such as on the lower limb.
Initially we hoped only a single TSE treatment would be required but, as with ECT, repeat treatments appear to be more effective.

Thermofield treatment

Currently TSE and ECT are our most utilised sarcoid treatments but we also offer thermofield treatment. Application of heat (hyperthermia) achieves a similar effect as ECT but also offers several additional advantages. Heat not only increases uptake of drugs and potentiates their effects but also activates the patient’s immune system and directly damages tumour cells by suppressing new vessel growth and killing cancer stem-like cells.

It also has analgesic properties, increasing patient comfort. In contrast to ECT, thermofield treatments can be performed without general anaesthesia.

The electrochemotherapy equipment was funded by the RVC’s charity the Animal Care Trust (ACT). The tumour specific electroporation equipment was purchased by funds donated to the ACT by the Alice Noakes Memorial Charitable Trust. The thermofield equipment was purchased by funds donated to the ACT by EBM Charitable Trust.