Tracheal melanoma in a cat.

Extraocular melanocytic neoplasms are rare in cats and occur mainly in the skin and oral cavity. Tracheal neoplasms are also rare in cats, with lymphoma being the most commonly reported tumor. Here, we describe a tracheal melanoma in an 8-y-old spayed female domestic shorthair cat that died after 8 d of cyanosis, dyspnea, and wheezing. Radiographic and tracheoscopy findings were consistent with a mid-tracheal obstruction. Gross findings consisted of a poorly demarcated, pale-yellow, 28 × 16 × 15-mm mass that effaced and expanded most of the mid trachea and partially occluded the tracheal lumen. Histologically, the mass was a poorly demarcated neoplasm that effaced the tracheal mucosa, submucosa, hyaline cartilage, and muscle layer and was partially surrounded by the tracheal adventitia. The tumor infiltrated and disrupted the tracheal cartilage and partially occluded the tracheal lumen. Neoplastic cells were elongate or polygonal and arranged in interweaving bundles or well-defined groups supported by a delicate stroma. Nuclei were round-to-oval and often irregular, with finely stippled chromatin with a prominent nucleolus. Rare neoplastic cells had brown cytoplasmic pigment that was black on Fontana-Masson stain. The mitotic count was 11 in 2.37 mm2 (10 FN22/40× fields). Neoplastic cells had cytoplasmic immunolabeling for melan-A and PNL2, consistent with a diagnosis of melanoma.