Pulmonary Carcinoma Metastasis in a Feline Digit
Authors: Kirsch Francine , Braun Adriana , Viégas Sallis Eliza Simone , Zamboni Rosimeri , Brambatti Gustavo , Giordani Claudia , França Raqueli Teresinha 
Published: March 2020

Background: Primary pulmonary neoplasia is rare in domestic cats, with fewer than 1% of all tumors diagnosed in this species. Primary lung tumors have a high percentage of metastases, observed in up to 75% of cases in cats. The lung-digit syndrome is characterized by primary pulmonary neoplasms with metastases to the extremities of the limbs, mainly distal phalanges, possibly involving several digits and more than one limb. This report describes a case of pulmonary carcinoma metastasis in a cat digit.Case: A 16-year-old neutered female cat was showing increased volume of the fourth digit was examined at the University of Caxias do Sul veterinary clinic. The animal also showed signs of progressive weight loss, apathy and limping on the right thoracic limb. After clinical evaluation, the animal was sent for radiographic examination of the right metacarpal/phalangeal region and the thorax. A radiopaque structure was observed with discreet central regions of radiolucency, measuring approximately 3 cm in height, 3.4 cm in length and 2.4 cm in depth in the left caudal lung, suggesting neoplasia or pulmonary abscess. Digit image revealed osteolysis of the right and middle distal phalanx measuring 2 cm in height, 3 cm in breadth and 1 cm in length. In view of these radiographic changes, we performed fine needle aspiration cytology of the digit and a nodule in the region of the skeletal musculature of the right thoracic limb. Cytological evaluation revealed cells had cilia on their surface (compatible with respiratory epithelium). The cytologic findings of the fine-needle biopsy were suggestive of carcinoma. After stabilization, the digit was amputated. The material was sent to the laboratory of the Federal University of Pelotas for histopathological examination. Histological evaluation of a digital pulmonary carcinoma metastasis was confirmed. In view of the prognosis and clinical evolution of the disease, the caretaker chose euthanasia. Necropsy and histopathological evaluation of the lung and other organs were not authorized.Discussion: According to the literature, primary lung tumors have a high percentage of metastases, observed in up to 75% of cases in felines.The size of the tumor mass is associated with its metastatic potential, and lung tumors smaller than 1 cm in diameter usually do not present metastases.In the present case, the mass in the lung was greater than 1 cm in size and the animal already presented metastasis in the digit and in the skeletal musculature. In addition to the thoracic cavity, sites where metastases from lung tumors may occur include regional lymph nodes, skin, eyes, skeletal muscle, multiple abdominal organs, and digits. Cats with pulmonary carcinoma and digital metastasis have a median survival 67 days after diagnosis, with intervals of 6 to 122 days reported. Most patients are euthanized due to persistent symptoms of lameness, lethargy and anorexia or evolution of respiratory signs, in addition to the short survival time associated with poor quality of life. In the case reported here, euthanasia was performed after 40 days of diagnosis due to the worsening of the animal's clinical condition.The combination of radiographic, cytological and histopathological findings suggested a primary lung tumor with digit metastasis, also known as lung-digit syndrome. For felines with claudication or digital inflammation, the lung-digit syndrome should be included in differential diagnosis, even if the animal does not present clinical signs associated with the respiratory system. Primary pulmonary carcinoma should be considered in any middle-aged to elderly cat with digital disease.