Equine oncology cases in Chile

Equine neoplasias in Chile, as in the rest of the word, are rather uncommon. Nevertheless, skin neoplasias are the most frequent ones, including sarcoids, melanomas, squamous cell carcinomas [1].

Common clinical signs depend on the size and location of the masses, generally small bulging masses appear on face, neck, extremities and/perineal areas, and speed of growth and appearance will vary depending on the mass. There is no real sex or breed predisposition, but depigmented skin and advanced age are risk factors to develop melanomas and carcinomas. Definitive diagnosis should be based on histopathology results. Treatments such as surgical excision, cauterization, cryosurgery, radiation, electrochemotherapy (ECT) have been reported.

ECT is a newer treatment that generally involves intratumoral injection of chemotherapeutic drugs followed by repeated electrical current to increase intracellular drug concentrations and by this, increase exponentially cytotoxic effects in neoplastic cells [2].

In our experience, ECT with local injection of cisplatin or bleomycin alone can be a very good treatment option with excellent results after 1-3 treatments, with or without surgical resection (Fig. 1). Typically, 1-3 treatments, 2-4 weeks apart are required. More treatments (6-12) are needed with chronic and/or severe presentations [personal experience]. However, it is common to receive horses in very advanced stages of disease, with large tumors where ECT alone may not be effective or will require too many treatment sessions. In these cases, in small animals, the combination of ECT with other treatment modalities is very effective [3]. The use of intravenous bleomycin is generally recommended for all small animal cases, regardless of the size of the lesion. This route reaches an adequate distribution and concentration of the drug in the tumor and its margins, avoids leaving areas of the tumor with insufficient drug concentration due to errors in the intratumoral administration technique, drug administration is safer for the handler, by itself it is an immune system activator, contributing to the local immune response induced by the treatment [3].

In horses the use of the IV route of bleomycin is costly considering the high volumes of drug required, and little evidence about the safety of the drug in this species. Also, the IV route should be avoided in animals that may be destined for human consumption.

We have used systemic bleomycin as an adjuvant chemotherapeutic approach in patients with large skin neoplasias (2 patients with sarcoids Fig.2, 1 patient with perianal melanomas). Results have shown that the treatment of ECT combined with local and intravenous administration of chemotherapeutic drugs in horses was well tolerated and successful in treating chronic and large fibroblastic sarcoids and melanomas, after 2-4 treatment sessions. Although this treatment approach is costly and must be performed under general anesthesia, increased treatment efficacy implies less treatment sessions.

ECT in conjunction with local and/or intravenous chemotherapeutic drugs is certainly a promising treatment approach for equine skin neoplasias. Nevertheless, further studies with larger sample sizes are required to reach consensus about the use of this rather newer therapy approach in horses.

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