Unusual multifocal pulmonary neoplastic lesions in a cat

An 8 years old castrated male stray cat, daily fed and looked after by feral cat caretakers was found death near the feline colony where it lived. The body was referred to the University of Milan for the necropsy. The cat was severely dehydrated, had lost incisives with severe gingivitis and abundant tartar accumulation and presented a shrunken, reduced in volume, left eye (phthisis bulbi). The most relevant alterations, affecting the abdominal and thoracic organs, were renal papillary erosion and necrosis associated to irregular renal profile with severe scarring and yellowish, pale cortex with numerous cortico-medullary strikes, and severe pulmonary atelectasis of the caudal lobes. Two pearly white, rounded, flat lesions, less than 1 cm in diameter, were detected in the left and right caudal lobes. Histologically, pulmonary lesions consisted of numerous, well circumscribed, not encapsulated nodules composed of irregularly arranged, tubular and/or dilated acinar structures, lined by a single layer of tall, columnar epithelial cells with abundant clear cytoplasm and basally located nuclei. Mitosis were less than 1 for HPF and anisokaryosis and anisocytosis were mild. Renal lesions were bilateral and diffuse. Histologically, they consisted of ulceration and necrosis of the papilla, numerous perivascular to interstitial aggregates of lymphocytes and plasmacells associated to severe interstitial fibrosis, glomerular synechiae/sclerosis and tubular degeneration, necrosis and mineralization. A diagnosis of end stage kidney, the most likely cause of death, was posed. Immunohistochemical investigation for thyroid transcription factor-1 (TTF-1), AE1/AE3 cytokeratins (CKs), CK5, smooth muscle actin (-SMA) and histochemical staining with PAS and alcian blue (AB) (pH 2.5) was performed. Neoplastic glands were diffusely positive for CKAE1/AE3, CK5 and PAS. AB staining was faint and multifocal, while TTF-1 and -SMA were negative. Based on histological and immunohistochemical findings, a diagnosis of mucus gland adenoma was formulated. Lung tumors, namely bronchial gland carcinoma, bronchiolo-alveolar tumors and squamous cell carcinoma, have been extensively reported in cats, even though they are overall considered rare tumors. Conversely, to the authors’ best knowledge, pulmonary mucus gland adenoma has not been reported to date in the feline species. In human beings, mucus gland adenomas are extremely rare tumors, arising mostly within the main, lobar or segmental bronchi and more rarely in the lung periphery. They are often endobronchial and multicystic, causing signs and symptoms of obstruction. The present report described the first case of peripheral lung nodules arising from the submucosal mucinous gland in a peripheral small airway in a cat, an unusual and rare benign lesion that shares many similarities with the human counterpart