Primary Lung Tumors in Dogs (Lung Cancer, Pulmonary Neoplasia)
Dr. Erika de Papp
Complete history and physical exam. A thorough history is always important in establishing a list of possible diagnoses. A physical exam may reveal abnormal or muffled lung sounds in animals showing signs of dyspnea. Careful auscultation of the heart will also help rule in or rule out heart disease as a likely cause of the signs. Many animals with fungal infections will also have enlarged lymph nodes or skin lesions.
Complete blood count. A CBC evaluates the red and white blood cells as well as the platelets. These parameters are often normal in patients with lung cancer, but will help exclude the likelihood of infectious causes of the clinical signs.
A biochemical profile evaluates blood sugar, blood proteins and electrolytes, as well as providing information about liver and kidney function. This is useful to get an overall idea of systemic health, and may guide further diagnostic testing.
Urinalysis. Evaluation of the urine is part of a complete laboratory assessment and gives a better indication of kidney function than the biochemical profile alone.
Chest radiographs. X-rays of the chest are probably the single most useful diagnostic tool in making a preliminary diagnosis of lung cancer. Most lung tumors are single masses that can be easily seen on routine X-rays of the chest. X-rays also evaluate for the presence of fluid in the chest cavity, the size of the heart and associated blood vessels, and the rest of the lung tissue.
Abdominal X-rays or abdominal ultrasound exam. Imaging studies of the abdomen may not be required in every case, but evaluation of the abdominal organs is a good screening test for evidence of metastasis of a primary lung tumor to other sites. Although many tumors spread from other sites to the lungs, primary lung tumors can spread throughout the lungs, as well as to other sites in the body.
Fine needle aspirate of the lung mass. If there is a mass that is big enough and close enough to the chest wall, an aspirate of the mass may be attempted with a hypodermic needle and syringe. This involves passing a needle through the chest wall and inserting it into the mass, then gently creating suction on the syringe to remove microscopic cells for evaluation. This is a fairly safe procedure, but should be done using ultrasound guidance to determine the exact location of the mass. The pet may also need to be sedated to perform this safely.
This procedure is most commonly done at specialty hospitals. If the patient has pleural effusion, this can be safely and routinely removed from the chest without ultrasound guidance. Removal of fluid may reduce the work of breathing as well as providing fluid for analysis and possible diagnosis. These methods may allow the doctor to make a diagnosis without undertaking a more invasive procedure, but it should be noted that a sample from a fine needle aspirate is never as good as a piece of tissue for biopsy evaluation.
Trans-tracheal aspirate or bronchoscopy. A trans-tracheal aspirate is a procedure in which sterile fluid is introduced into the trachea and fluid and cells are suctioned out. This can sometimes be another useful method to obtain a diagnosis. However, this is often more useful if there is evidence of widespread lung disease rather than a single mass. This test can be performed under light sedation. A bronchoscopy study involves placing a scope into the trachea and smaller airways. The interior of the airways can be examined by this method and samples can also be obtained for analysis. Single masses in the lung tissue cannot be seen via this method, but a mass associated with one of the airways may be sampled using this technique.
Mass biopsy. Tissue samples from a lung mass are often the only definitive method for making a diagnosis of lung cancer. The most common procedure to obtain a sample of the mass is exploratory thoracotomy, which involves opening the chest cavity surgically. Often the mass can be completely removed with this method. Therefore, surgery can play both an important diagnostic as well as therapeutic role in management of the disease process. A second potential way to obtain a lung mass biopsy is by thoracoscopy. This procedure is performed using a scope, which is placed into the chest through a smaller incision than what would be used for surgery.
The scope is a long tube with an attached camera, which allows visualization within the chest cavity. Depending on mass location, a biopsy may be taken using this method. However, it is unlikely that the mass could be removed using the scope. Finally, in certain cases, ultrasound guided biopsies may be performed. This is the least invasive way to obtain a biopsy, but the yield is lower with respect to sample size, and it may be a more risky procedure.
Surgery is the treatment of choice for animals with primary lung tumors. Depending on the size and location of the mass, complete removal may or may not be possible. If there is evidence of widespread involvement, surgical removal is generally not an option. In most cases of single lung tumors, the lung lobe that is involved is totally removed with the mass.
Depending on the type of tumor, chemotherapy may be recommended in addition to surgery. If surgery is not feasible due to extent of disease, chemotherapy may slow the progression of disease. However, there is little evidence to show that chemotherapy is very effective in most primary lung cancers.
Optimal treatment for your pet requires a combination of home and professional veterinary care. Follow-up can be critical, especially if your pet does not improve over the expected time frame.
If your pet undergoes a thoracotomy, hospitalization will be required for at least several days post-operatively. This is a complicated surgery done only at referral hospitals. Careful post-operative monitoring is required. Most animals will have tubes placed in the chest during surgery to drain fluid that may form following the procedure. Tubes also help evacuate air from around the lungs. Your pet will only be sent home when the lung function appears stable.
Once at home, your pet will need to be carefully monitored for labored breathing or abnormal posture, which may indicate an increased effort to breathe. Animals having difficulty breathing will often extend the head and neck, and hold their front limbs away from the body. They may be reluctant to lie down, as this may increase their respiratory effort.