A research project funded by The Horse Trust has found that various types of ocular tumours can be successfully treated with mitomycin C, a cytotoxic antibiotic isolated from a bacterium.

The research concludes that mitomycin C offers a safe and cost effective alternative to current treatment options such as surgery and radiation.

The research project was led by Fernando Malalana, while working as The Horse Trust's Clinical Scholar in Equine Internal Medicine at University of Liverpool. Fernando is now working as a Clinician Teacher in Equine Internal Medicine at the university.

Ocular tumours are more difficult to treat than tumours in other parts of the horse's body due to the risk of damaging the eye. In the study, Malalana investigated the use of mitomycin C in treating ocular squamous cell carcinoma, the most common ocular tumour in horses, and occular sarcoids, skin tumors that frequently affect the eyelids .

Mitomycin C is an antibiotic isolated from a bacterium, Streptomyces caespitosus. It is known to have cytotoxic effects and has been used to treat tumours in horses before, but only in combination with surgery.

Currently, the main method of treating ocular squamous cell carcinoma is by removing the tumour surgically or with radiation. Both treatments are costly and have a number of associated risks. There is also the risk of damage or scarring to the eye.

Fourteen horses with ocular squamous cell carcinoma, three of which were affected bilaterally, were included in the study. Mitomycin C was applied to the conjunctival sac of the affected eye; in some of the cases the treatment was combined with surgery. Malalana found that of the 8 eyes treated with mitomycin C alone, clinical resolution occurred in 6 cases. Of the 9 eyes treated with both surgery and mitomycin C, clinical resolution occurred in 7 cases.

Mitomycin C was also used to treat various types of sarcoids found in the eye. Currently, the most effective treatment for occular sarcoids is radioactive wire. However, radioactive wire treatment is not ideal as it is expensive, only offered in two locations in the UK, and has potential health risks to the vet applying the wire due to exposure to radioactivity.

Six horses and two donkeys with occular sarcoids, including one horse that was affected bilaterally, were treated with mitomycin C, which was injected directly into the tumour. Malalana found that of the nine nodular and fibroplastic occular sarcoids treated with the antibiotic, all were completely cleared. However, the vets did not have good results with verrucous sarcoids.

Malalana said: "The results of this research should offer hope to the owners of horses that have eye tumours. We have already been contacted by vets from across Europe to find out more information about this treatment and hope that it will be offered to more horses with occular tumours in the future".

Vets at the University of Liverpool are now testing the use of mitomycin C on other tumours that are difficult to treat surgically, including melanomas near the horse's anus. So far, two cases have been treated, but it is too early to tell whether treatment has been successful.

Malalana's research has been submitted to Veterinary Ophthalmology journal.

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