Tumours of the equine bladder: What makes treatment of these cases so difficult?

challenging and often fatal cancer. In this issue, Serena et al. (2009) describe a partial cystotomy to treat a squamous cell carcinoma of the bladder wall, the first documented successful removal of a tumour of this nature. Historically, treatment of neoplasia of the urinary bladder in horses, and other domestic animals for that matter, has been limited. How do these cancers typically present? What is it about these particular tumours that makes treatment so difficult? Which treatments have proven to be successful and which have not? The following is an attempt to summarise the major areas of research and advancements in the treatment of equine bladder tumours. The most common urinary tract neoplasmia in equines, especially those in the older age range as that of the mare in Serena et al.’s (2009) case, is squamous cell carcinoma, followed by transitional cell carcinoma (Cornelisse 2003). Other infrequent reports include lymphosarcoma (Sweeney et al. 1991), fibromatous polyp (Fischer et al. 1985), rhabdomyosarcoma (Turnquist et al. 1993) and leiomyosarcoma (Hurcombe et al. 2008). The poor prognosis that accompanies these tumours is in large part due to their tendency to metastasise to other organs. This may occur through direct invasion into the abdominal cavity, via the lymphatic system, or haematogenously in advanced cases (Fischer et al. 1985). Common clinical presentations of a bladder neoplasm resemble urolithiasis or cystitis. Haematuria, which may include blood clots (Fischer et al. 1985), stranguria and pollakiuria are the most common signs (Traub-Dargatz 1998). The haematuria is thought to result from erosion and damage to the bladder mucosa at the site of the neoplasm. Increased frequency of urination is thought to be the result of cystitis and decreased bladder volume due to the infiltrative mass, although there has been some thought that chronic cystitis may be the primary cause of the neoplasia (Traub-Dargatz 1998). Other signs seen less frequently include weight loss and anorexia. Laboratory tests may show azotaemia and mild anaemia (TraubDargatz 1998). Complications can arise due to obstruction by the mass and may include pyelonephritis and ureteral dilatation leading to hydronephrosis (Cornelisse 2003). Differentiation between neoplasia and urinary calculi can be made by a combination of rectal palpation (a bladder stone should be much firmer on palpation), ultrasonography (a bladder stone would be more hyperechoic), endoscopy and biopsy (Traub-Dargatz 1998). Use of chemotherapeutic drugs in the treatment of equine neoplasia is not common. Reasons for this include the high cost of the drugs due to large body mass, requirement for specialist knowledge and hospitalisation for drug administration, undesirable side effects, poor success rate, and often late diagnosis of neoplasia (Knottenbelt 2006). Nevertheless, there are case reports of treatment of bladder tumours with cytotoxic agents. Fischer et al. (1985) documented infusion of 5-fluorouracil into the urinary bladder of a pregnant mare for 4 consecutive days, followed by 4 more treatments every other day. Initially, haematuria decreased significantly and the mass took on a more fibrous consistency. However, within 2 weeks of the course of chemotherapeutics, the mare became severely anorectic, the mass doubled in size, and the owners elected to subject the animal to euthanasia. The authors postulated that if a urinary tract neoplasm could be diagnosed earlier, intralumenal chemotherapeutic treatment may be successful in limiting tumour growth. Monthly debulking of a squamous cell carcinoma in addition to intracystic administration of 5-fluorouracil has been reported to prolong survival in one mare for an additional 9 months (Cornelisse 2003). Hurcombe et al. (2008) treated leiomyosarcoma in a 2-year-old filly with a combination of doxorubicin, diphenhydramine and dexamethasone sodium phosphate. Less than 2 weeks later, the mucosa appeared less inflamed, but the mass had grown so large that it filled the bladder lumen and the horse was subsequently subjected to euthanasia. In the case of Serena et al. (2009), resection of the tumour was followed by piroxicam 267