A research project funded by leading British charity The Horse Trust has found that various types of ocular tumors can be successfully treated with mitomycin C, a cytotoxic antibiotic isolated from a bacterium. 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 the University of Liverpool. Fernando is now working as a clinician teacher in Equine Internal Medicine at the university.
Background on ocular tumors
Ocular tumors are more difficult to treat than tumors in other parts of the horse’s body because of the risk of damaging the eye. In the study, Malalana investigated the use of mitomycin C in treating ocular squamous cell carcinoma, which are the most common ocular tumors in horses, and occular sarcoids, which are skin tumors that frequently affect the eyelids .
Mitomycin C is an antibiotic isolated from a particular species of bacterium, known as Streptomyces caespitosus. It is known to have cytotoxic effects and has been used previously to treat tumors in horses before, but only in combination with surgery.
Currently, the main method of treating ocular squamous cell carcinoma is by removing the tumor surgically or with radiation. Both treatments are costly and have a number of associated risks. For example, the horse needs to be anaesthetized for surgery and there is a 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 eight eyes treated with mitomycin C alone, clinical resolution occurred in six cases. Of the nine eyes treated with both surgery and mitomycin C, clinical resolution occurred in seven 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 veterinarian applying the wire because of 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 veterinarians did not have good results with the antibiotic when treating verrucous sarcoids.
“The results of this research should offer hope to the owners of horses that have eye tumors. We have already been contacted by veterinarians from across Europe to find out more information about this treatment and hope that it will be offered to more horses with occular tumors in the future,” said Malalana.
Vets at the University of Liverpool are now testing the use of mitomycin C on other tumors 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 and also will appear in The Veterinary Record .
To learn more:
F.C. Malalana, D. C. Knottenbelt, S. A. McKane. Mitomycin-C, with and without surgery, for the treatment of equine ocular squamous cell carcinoma. Veterinary Record. (in press)
About The Horse Trust:
The Horse Trust, founded in 1886, is the oldest horse charity in the UK. Until a recent name change, it was known as The Home of Rest for Horses. Based at Speen, Buckinghamshire, The Horse Trust provides a place of retreat for working horses that have served their country or community and nurtures them throughout their final years. The charity also gives sanctuary to horses, ponies and donkeys that have suffered and need special treatment. The Horse Trust funds non-invasive research that advances knowledge of equine diseases, improving diagnosis and treatment and reducing suffering among equines worldwide. The charity also offers training for professionals and owners, with a focus on equine welfare and quality of life assessment.
by Fran Jurga
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