Equine Health Update Issue 2 Volume 19 - Page 31

EQUINE | CPD Hyperthermia is an easy, convenient and cost-effective adjunctive therapy and but limited by the fact that only small foci <1 cm in diameter can be treated per applica- tion. is marked increased to in the region of ± 90%. Compli- cations with larger tumours is that follow-up reconstruc- tive blepharoplasties or corneo-conjunctival surgeries are frequently required. • Radiation Therapy Radiotherapy is considered when surgical excision would have an unacceptable functional outcome. Inhibition of tumor growth by radiation depends on tumor volume, mitotic activity and location. Fast-growing tumors are more responsive to radiation than slow-growing masses. Surgery should be combined with radiation, if possible, to minimize the radiation dose. Penis and Prepuce Occular SCC of the orbit arise most commonly from the edge of the third eyelid followed by the limbal conjunctiva. Lack of eyelid and conjunctival pigment and exposure to UV radiation are considered important predisposing fac- tors. In 15 - 20 % of cases bilateral involvement may be seen. All breeds of horses may be affected but there is an apparent breed predisposition in heavy draft horses. The mean age of affected animals is approximately nine years. Therapy may influence the prognosis, but even untreated neoplasms are usually slow to metastasize (in such cases usually only to the local lymph nodes). In one retrospective study 10 - 15 % of squamous cell carcino- mas exhibited regional or distant spread. At this site, SCC develops through a series of pre-malig- nant stages (plague, papilloma) to squamous cell carci- noma in-situ and eventually invasive SCC over several months or years. Spontaneous regression of these pre- malignant stages is reported in ± 25-50% of cases. Treatment Surgery alone with complete local excision has a ± 50% success rate. When used in conjunction with cryothera- py, hyperthermia or local chemotherapy the success rate SCC of the penis and prepuce occurs with equal frequen- cy in stallions and geldings with an average age of onset of 12 years or older. Squamous papilloma is considered a pre-neoplastic lesion with progression from plaque to papilloma to invasive SCC. Equus caballus papillomavi- rus-2 has been implicated as a promotion factor for SCC at this site. The head of the penis is the most common location for neoplasia with ulceration and necrosis be- ing common. Shaft of the penis and prepuce are less common while the scrotum is a rare location. Invasion of the corpus cavernosum and metastasis to the ingui- nal lymph nodes is common. Further spread to other organs such as the lung and the liver is less frequent. Treatment • Surgery is considered an effective option with larger tumours. Partial phallectomy has been effective only in cases where SCC is confined to the glands and/or body of the penis and there is no proximal spread or involvement of regional lymph nodes. • Topical fluorouracil is reported to have a ±90% suc- cess rate for early small SCC lesions on the penis / pre- puce. Fluorouracil is retained in the prepuce for 10–14 days, facilitating treatment at this site. • Cryotherapy is best used for early pre-cancerous le- sions of the penis and prepuce, as it only penetrates a short distance beneath the skin. Guttural Pouch Squamous cell carcinoma has been reported to arise within the squamous epithelium of the guttural pouch of aged horses. Tumours are frequently associated • Volume 19 no 2 • June 2017 • 31