Malignant anal sac melanoma in dogs: eleven cases (2000 to 2015).

Objectives: To report the signalment, clinical presentation, treatments pursued and outcomes of dogs with malignant anal sac melanoma.

Methods: Medical records from five institutions from January 2000 through December 2015 were reviewed and dogs with cytologically- or histologically-confirmed malignant anal sac melanoma were identified. Signalment, clinical signs, staging, cytology, histopathologic analysis, surgical and non-surgical treatments were extracted from the medical records. The referring veterinarians and owners were contacted for follow-up data.

Results: Eleven dogs were included and survival data was available for all. The most common clinical signs were bloody anal sac discharge and perianal licking. Initial treatments pursued included surgery (n=8), chemotherapy (n=1), and palliative treatment with pain medications and stool softeners (n=2). In an adjuvant setting, melanoma vaccine was pursued following surgery in three dogs and chemotherapy in one dog. Regardless of treatment, progression-free survival (mean 92 · 5 days) and overall survival times (median 107 days) were short.

Clinical Significance: Dogs in this case series had a guarded to poor prognosis regardless of treatment. Ten of 11 dogs were euthanased due to local or distant disease progression. Only 1 of 11 dogs was alive one year after diagnosis. An understanding of tumour behaviour in this location could lead to improved survival times with earlier diagnosis and treatment.