Gastric mucinous adenocarcinoma with cutaneous metastases in a dog: diagnosis by fine-needle aspiration cytology

A 12‐year‐old, intact, male mixed‐breed dog was presented with anorexia, vomiting and multiple cutaneous nodules on its neck, trunk and hindlimbs. Fine‐needle aspiration cytology of the nodules was characterised by a pleomorphic population of cells arranged singly or in small cohesive clusters, embedded in an amorphous mucinous material stained positive by periodic acid‐Schiff (PAS). Acinar structures were occasionally found. Cells appeared either small with scant basophilic cytoplasm or large with a histiocytic appearance. Large cells had cytoplasm filled with a PAS‐positive granular material. A presumptive diagnosis of cutaneous metastases of a mucinous adenocarcinoma was made. A primary, gastric, signet‐ring mucinous adenocarcinoma was confirmed postmortem examination and by histopathology. To the authors' knowledge, this is the first report of a gastric mucinous adenocarcinoma with cutaneous disseminated metastases in a dog.