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.