Multi-institutional retrospective study of canine foot pad malignant melanomas: 20 cases.

Melanomas arising from the foot pad are a rare clinical entity in dogs. The biologic behaviour of foot pad malignant melanoma is not well understood, and these tumours are infrequently described. The objective of this study was to evaluate the clinical characteristics of primary canine foot pad melanoma in a larger cohort of patients. Eligible cases were solicited from the American College of Veterinary Internal Medicine (ACVIM) Oncology listserv for retrospective review. Included dogs had a cytologic and/or histologic diagnosis of foot pad melanoma evaluated by a board-certified clinical or anatomic pathologist. Dogs with cutaneous, oral, digital, subungual or interdigital melanomas were excluded. A total of 20 cases were included. Eleven dogs received various adjuvant therapies including chemotherapy, radiation therapy, and/or the ONCEPT canine melanoma vaccine following surgery. At diagnosis, regional lymph node metastasis was observed in four dogs (20%). Seven dogs developed subsequent regional and/or distant metastasis for an overall metastatic rate of 55%. The progression-free interval (PFI) was 101 days (range, 20-960 days). The median survival time (MST) was 240 days (range, 25-479 days). For dogs receiving adjuvant therapy, the MST was 159 days (range, 25-387 days). Canine foot pad melanoma is a rare neoplasm that can exhibit an aggressive behaviour.