Overview of Lung Cancer in Dogs
Primary lung tumors are cancers that arise in the lung tissue of both dogs and cats. They are rare in both species, but slightly more common in dogs.
The most common type of tumor is a carcinoma. Carcinomas are malignant tumors that develop from the epithelial tissues in the lungs. They may be primarily derived from the lung tissue itself, or the airways or bronchioles.
The exact cause of lung cancer is not known, but there appears to be an increased incidence of cancer in dogs that live in urban environments, as well as dogs that are exposed to second hand smoke. Lung cancer is generally diagnosed in older animals, with an average age of about 11 years, but it can also be seen in younger pets.
There are no known predispositions with respect to breed or sex and the development of lung tumors. However, most lung cancer is seen in medium to large sized dogs.
What to Watch For
Signs of lung tumors in dogs may include:
Chronic (long term) coughing
Coughing up blood
Anorexia (lack of appetite)
Diagnosis of Primary Lung Tumors in Dogs
Complete history and physical exam
Complete blood count (CBC)
Chest radiographs (X-rays)
Abdominal radiographs or ultrasound exam
Fine needle aspirate of lung mass
Trans-tracheal aspirate or bronchoscopy
Treatment of Primary Lung Tumors in Dogs
Surgical removal of the lung tumor
Chemotherapy may be recommended in selected cases.
Monitor breathing patterns and monitor for recurrence of original clinical signs. Avoid exposure to second hand smoke.
In-depth Information on Primary Lung Tumors in Dogs
The most common clinical sign seen in patients with lung tumors is a chronic cough. Usually this is a non-productive cough, which means the pet is not coughing up fluid or mucus. Occasionally pets will cough up small amounts of blood. If the tumor is large and is causing compression of the trachea or a major airway, the animal may experience dyspnea (difficulty breathing). Other causes of dyspnea associated with lung cancer include fluid accumulation around the lungs, known as pleural effusion, and widespread cancerous involvement of the lungs, leaving little normal lung tissue.
The clinical signs can also be vague and not specific to the respiratory tract. Up to 25 percent of pets with lung cancer may not show any clinical signs of illness. Occasionally dogs and cats with lung cancer are lame. This can occur because of spread of tumor to the bones of the limbs (more common in cats), or due to a secondary effect that the tumor has on bone growth (more common in dogs). The latter condition results in excess bone growth and swelling of the limbs, and is referred to as hypertrophic osteopathy. Several other conditions may cause similar clinical signs to those seen in animals with lung cancer. These include:
Heart failure. Heart disease and more commonly heart failure, are common causes of chronic coughing in dogs. Dogs that are in heart failure also experience dyspnea due to fluid accumulation in the lungs.
Pneumonia. Bacterial infections in the lungs will often cause coughing and dyspnea. This is more common in dogs, but also seen in cats.
Metastatic cancer. Cancer that starts in one organ and spreads to other parts of the body is known as metastatic disease. The lungs are a common site of metastasis for many cancers, and the clinical signs may mimic those seen with primary lung tumors.
Heartworm infection. Heartworms affect both the heart and the lungs, and may cause coughing and dyspnea in affected animals. This is more common in dogs.
Fungal infection. Fungal infections are common in many of the Midwestern, Southeastern, and Southwestern states. Two fungal infections that can severely affect the lungs and produce coughing and dyspnea include Blastomycosis and Coccidioidomycosis. These infections usually affect multiple organ systems and are more common in younger animals.
Lungworms. These are parasitic worms that have a predilection for living in the respiratory tract, and can affect both dogs and cats.
Collapsing trachea. Physical collapse of portions of the trachea is a common problem in small breed dogs. It causes a characteristic honking cough and may causes episodes of respiratory distress.
In-depth Information on Diagnosis
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.