Cancer in dogs can occur in any location in the body. However, the chest, or thorax, is a common location for cancer in dogs. Tumors that begin within the structures of the chest include cancers of the lung, heart, lymph nodes and thymus gland. In addition, tumors that begin in other locations in the body commonly spread to the lungs, a process known as metastasis. Depending on what type of cancer is present, dogs can exhibit a variety of symptoms associated with chest tumors. If you notice any of the symptoms discussed, seek care from your veterinarian.
Primary Chest Tumors
Primary tumors of the chest begin in the lungs, heart, lymph nodes, or thymus gland. Primary lung tumors arise within the lung tissue itself and may cause increased breathing rate, effort or cough. Tumors of the heart may cause bleeding or fluid accumulation around the heart, creating a condition known as pericardial effusion, which appears as a very enlarged heart on X-rays or CT scan. Pericardial effusion often leads to an elevated heart rate and weakness and can progress to collapse if it is severe.
Lymph nodes in the chest are located in front of and above the heart. These Lymph nodes may become enlarged due to primary lymphoma, leading to increased breathing rate, cough, or fluid accumulation around the lungs. Another common tumor that occurs within the thorax is thymoma, a tumor of the thymus gland. These tumors also occur as large masses in front of the heart and can cause the same symptoms as enlarged lymph nodes.
Your veterinarian may recommend thoracic X-rays, a CT scan of the chest, and aspirates to collect fluid or tissue from the lesion to obtain a diagnosis. Ultimately the diagnosis will determine if your dog should be treated with surgery, radiation therapy or chemotherapy -- or a combination -- for the best outcome.
Metastatic Chest Tumors
Tumors that spread to the lungs from another site in the body are termed metastatic tumors. Metastatic tumors grow within the lung tissue itself after traveling to the lungs through the blood or lymph system. Many types of cancer in dogs will spread to the lungs, but some of the more common types include melanoma, osteosarcoma, hemangiosarcoma, and mammary tumors. Primary lung tumors can also spread to other parts of the lung and create metastatic lesions, while some tumors metastasize to the lymph nodes in the chest.
Metastatic disease in the lung presents as multiple nodules found in different parts of the lungs. Metastasis to the lymph nodes will create a mass effect in front of or above the heart due to enlargement of the nodes. Clinical signs of metastasis include increased breathing rate and effort, cough, loss of energy or appetite and possibly weight loss.
Chest X-rays are the most common tool used to diagnose metastasis to the lungs or lymph nodes in the chest. A CT scan can provide further information if there is a question about the origin or number of lesions. If X-rays show lesions consistent with metastatic disease, your veterinarian will likely recommend tests to look for the location of the primary cancer.
Treatment and Prognosis
Primary chest tumors may be treated with surgery to remove the mass and additional therapy may be recommended, depending on the diagnosis. Metastatic tumors are more difficult to treat once they begin showing up within the chest. Your veterinarian will be able to provide you with the most accurate information regarding treatment options and prognosis based on your dog's case.