Solitary pulmonary metastasis at presentation in a dog with anal sac adenocarcinoma without nodal metastasis

A 10-year-old, male, neutered labrador retriever was diagnosed with a left-sided anal sac adenocarcinoma. At diagnosis, staging with an abdominal computed tomography revealed no intraabdominal lymph node enlargement. Thoracic radiographs revealed a soft tissue pulmonary nodule with cytology consistent with a carcinoma. The dog underwent a left anal sacculectomy, and re-presented 24 days later for a lung lobectomy in which histopathology represented primary anal sac adenocarcinoma metastasis. Forty-nine days after initial presentation, the dog was referred for a right distal radial lytic lesion in which cytology was concerning for osteosarcoma. After 132 days of initial presentation, an abdominal ultrasound revealed normal-sized iliosacral lymph nodes. The dog was humanely euthanased 446 days after initial diagnosis. This case report describes a dog who had a solitary metastatic pulmonary nodule from apocrine gland anal sac adenocarcinoma at the time of presentation with no nodal metastasis identified, which is atypical compared to previous reports.