Lung tumors in cats and dogs

Lung tumors that arise from lung tissue are called primary tumors. If lung tumors have spread to the lungs from a tumor arising in another organ, they are called secondary tumors. Most tumors of the lungs are secondary. Lung tumors can occur as single or multiple masses, and they can involve one or several lobes. Older animals are most commonly affected. Most tumors are malignant, and carcinoma is the most common type. Benign tumors are rare. It is possible that passive cigarette smoke and genetic factors influence the development of lung tumors.

About 25 percent of dogs with lung tumors have no clinical signs. Coughing and panting, with or without some degree of respiratory distress, are common. Exercise intolerance may be observed. Dogs with advanced disease will have a decreased appetite and weight loss.

Lung masses may be found incidentally when X-rays of the chest are taken for some other reason. Routine chest X-rays usually reveal masses in the chest if they are of a significant size. If a lung tumor is suspected, three views of the chest are often necessary to identify and confirm the locations of the masses. X-rays may also reveal fluid in the chest cavity and enlargement of the lymph nodes in the chest. A definitive diagnosis of lung tumors requires biopsy of the tumor. Depending on the location within the chest, biopsy may be done through the chest wall with ultrasound guidance or sometimes via bronchoscopy under general anesthesia or by open chest surgery. A thorough search of the rest of the body for other tumors in organs is also necessary, as most of these lung tumors are secondary tumors that have spread to the lungs from other organs.

Surgical removal of the tumor by lobectomy is the treatment of choice for solitary tumors, especially if they are believed to be primary lung tumors. Chemotherapy may be tried to decrease the size of metastatic tumors in the lungs. The most important factors in determining prognosis are the tumor type and whether it is spread to other lung lobes or to the lymph nodes. Prognosis is grave for animals with metastatic lung tumors.

Dr. Karsten Fostvedt is a veterinarian at St. Francis Pet Clinic in Ketchum.

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