A variety of therapies are employed in the management of anal sac apocrine gland adenocarcinoma (ASAGA), including surgery, radiotherapy and chemotherapy. Toceranib phosphate (Palladia®) has shown anti-cancer activity in dogs with advanced ASAGA, which may be related to receptor tyrosine kinase expression such as KIT, RET and PDGFR.

Whilst some patients present with advanced regional nodal metastases (typically to the iliosacral lymphatic centre; stage 3b), unfortunately some present with distant metastases which can temper owners' desire to choose aggressive loco-regional therapies including lymph node extirpation or radiotherapy. Indeed such therapies would also not treat the distant metastatic deposits and so systemic therapy would still be a requirement for successful management.

Fifteen dogs presented between 2012 and 2016 with stage 4 ASAGA (presence of distant metastases) with no prior therapy, other than in two patients where the primary tumour in the anal sac had been surgically excised as a diagnostic procedure.

Presenting clinical signs were related to abnormal defaecation in only eight patients with other dogs diagnosed due to incidental discovery for another problem (n=4), PUPD (n=1) and spinal pain (n=2).

A variety of breeds were represented, though 40% were English Cocker Spaniels. All dogs had lymph node metastasis. Other sites of metastasis included lung (n=11), liver (confirmed in n=4 and highly suspicious in n=3), lumbar spine (n=2) and kidney, skin and peritoneum (all n=1).

The median toceranib dose was 2.4 mg/kg (range 2.1–2.6) and was administered on a Monday-Wednesday-Friday basis. Concurrent medications were firocoxib (n=5), carprofen (n=1) and prednisolone (n=1); the latter being for management of concurrent hypercalcaemia of malignancy. No serious toxicities were seen during toceranib therapy. Three episodes of haematological toxicity (grade I anaemia, n=2; and transient mild thrombocytosis, n=1) were seen. One dog experienced an episode of grade 2 diarrhoea, necessitating a short treatment break and re-institution at a lower dose.

Routine repeat staging was advised, and when performed a reduction in tumour burden (but classified as stable disease) was seen in all but one patient where progressive disease was observed.

Median survival time of toceranib-treated patients was 359 days (range 66–1024 days), which is substantially higher than 71 days (median, 95% CI 6–136 days) or 82 days (95% CI 0–247 days) previously reported with a variety of non-TKI therapies.

Toceranib phosphate can be a successful and well-tolerated monotherapy for dogs with stage 4 ASAGA.

Disclosures

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