Primary Lung Tumors in Dogs

Primary lung tumors are rare in canines, accounting for only 1% of all tumors in dogs. Pulmonary tumors that do develop in dogs are frequently malignant and require invasive surgery to correct. Dogs with a single tumor have a good chance of surviving with prompt medical intervention if the cancer has not had an opportunity to spread, however, if multiple tumors are present or if the cancer has spread the outcome may be more guarded. If you suspect that your pet may have lung cancer, it is crucial to get it diagnosed as early as possible.

Primary lung tumors, also known as pulmonary tumors, are frequently malignant and require surgery to remove both the growth and a significant portion of the lung.

The symptoms of lung cancer can vary somewhat depending on where the cancer is located in the lung and how quickly the tumor or tumors are growing. Common signs of canine lung cancer can include: 

• Bloody cough
• Chronic cough
• Difficult respiration
• Lethargy
• Loss of appetite
• Reluctance to exercise
• Weight loss
• Wheezing

Types

• Adenocarcinomas - This type of tumor is made up of epithelial tissue, but it has a glandular origin and glandular characteristics
• Anaplastic carcinomas - These are malignant tumors comprised of epithelial origin, or that show epithelial characteristics, but without the cellular or physical characteristics of other identified types of cancer
• Bronchial, bronchioalveolar, and alveolar carcinomas - These are tumors made up of epithelial cells and found in the bronchi (bronchial) or alveoli (alveolar) of the lungs, or in both (bronchoalveolar)
• Squamous cell carcinomas - Epithelial cells of a squamous nature make up these tumors, which are more commonly found on surface areas such as the head, neck, cervix, or anus, but can invade the bladder, esophagus, prostate, or lungs as well

Just as with human cancers, the origins of canine cancers are not fully understood but are known to have several possible origins. Lung cancer in dogs is more common in middle-aged or older dogs of either gender.  Dogs in urban environments are more likely to be diagnosed with primary lung cancer than rural dogs, but it is unclear if the urban environment is contributing to cancer rates or if the cancer of urban dogs is just more likely to be caught.  A few possible origins of lung cancer can include: 

• Genetic predisposition - The boxer breed is more likely than other breeds to develop lung cancer; other breeds that may be at an increased risk include Doberman Pinscher, Bernese Mountain Dog, Australian Shepherd, and Irish Setter   
• Second-hand smoke - Smoking is the predominant cause of lung cancer in humans, and second-hand smoke can affect our pets as well; dogs with short or medium snouts are more likely to develop lung cancer due to second-hand smoke, whereas dogs with long snouts are at an increased risk of cancers of the nasal passages 
• Asbestos - Exposure to asbestos can also cause certain types of lung cancers to develop in dogs just as it can for humans

When your veterinarian does a physical examination of your pet, she will be attempting to differentiate this disorder from disorders with similar symptoms, such as pneumonia, heartworm infection, or collapsing trachea. A complete blood count will help rule out other diseases, and a biochemical profile will help to evaluate the blood sugar levels and with the aid of the urinalysis will provide additional information on liver and kidney health.

At this point, the examiner may want to get a clearer picture of the lung area to see if any masses or malformations are present. Both x-ray technology and ultrasound imaging are valuable in the detection of the tumors themselves as well as evaluating the tissue health of the lungs and any fluids found in the chest cavity. Canine lung cancer most often shows as a single mass in the area of the lung that is furthest back in the body, called the caudal area of the lungs. A definitive diagnosis will usually be made by a fine needle aspirate type biopsy of the mass in the lungs.

The preferred treatment for lung cancer in dogs is the removal of the tumor or tumors. Approximately 80% of canine lung cancer cases are malignant, so the entire affected lobe or lobes of the lung are often removed in order to prevent the further spread of the disease. This is typically done through the side of the chest cavity using a procedure known as a lateral thoracotomy. In some cases, the positioning requires that a median sternotomy is performed instead, usually so that the surgeon can reach both the left and right side of the lungs. In some situations, an entire half of the lung needs to be removed.

The treatment after the removal of the lung tissue will be dependent on which type of cancer it is and how far it has spread from the lungs if it has. Chemotherapy may be used to slow the progression of pulmonary types of cancer, but has not been proven to be effective in all cases. Radiation therapy may also be used, provided that the tumor is not overly close to the heart. Drugs known as antiangiogenic medications are designed to prevent the formation of new blood vessels and may help to prevent the growth and spread of tumors.

Once the tumor and surrounding tissues have been removed, and your pet has been cleared to go home, some specialized care will be required. Exercise will need to be limited for several weeks to prevent further damage to the respiratory system or surgical wounds. Dogs who undergo a median sternotomy surgery generally require about six weeks to heal enough for any exercise, however, those that were given a lateral thoracotomy may recover in as little as three weeks. You will want to contact your veterinarian if breathing becomes labored or if the tongue or gums lose color. This is major surgery, so pain medications will be required, and the incision will need to be monitored to prevent any infections from taking hold.