Lung Cancer in Pets is Serious, But Often Treatable

Lung cancer is the second most common cancer in both men and women (not counting skin cancer). In men, prostate cancer is more common, while in women breast cancer is more common.

Lung cancer accounts for just over 25 percent of all human cancer deaths and is the leading cause of cancer death among both men and women. Each year, more people die of lung cancer than of colon, breast, and prostate cancers combined.

Lung cancer is typically diagnosed in older patients, with two-thirds of individuals being age 65 or older. Less than two percent of all cases are found in people younger than 45.

The American Cancer Society’s estimates for lung cancer in the United States for 2015 are:

About 221,200 new cases of lung cancer (115,610 in men and 105,590 in women)

An estimated 158,040 deaths from lung cancer (86,380 in men and 71,660 among women)

Contrary to the disease in people, lung cancer is very rare in dogs and cats. The average age of dogs with primary lung tumors is approximately 11 years and the risk of developing lung cancer rises after the age of 13.

In cats, the average age at diagnosis is about 12 years, with most cats being more than 5 years of age. In both dogs and cats, no consistent breed or gender predisposition is found.

Pets with lung tumors often show adverse clinical signs, including a chronic non-productive cough, difficulty breathing, lethargy, and weight loss. Other less specific signs include fever, lameness, and, in cats, vomiting. Many pets are incidentally diagnosed with primary lung tumors while undergoing routine chest radiographs (x-rays) taken for other purposes.

Fluid may build up in the space around the lungs (pleural effusion) secondary to tumor cells invading into the lining surrounding the lungs or into lymphatic vessels. This can cause a pet to show signs of significantly labored breathing, which is a medical emergency.

Cats can experience a unique presentation of lung cancer where the primary tumor spreads to the bones of the digits (“toes”). In fact, some feline patients are diagnosed with the boney lesions prior to being diagnosed with a lung tumor. 

If a diagnosis of lung cancer is suspected, computed tomography (CT) scans of the chest are recommended to better delineate the size and location of the tumor. CT scans are also more sensitive than radiographs for picking up metastatic tumors within other lung lobes, enlarged lymph nodes, and other intrathoracic abnormalities that may be present.

Surgery is the treatment of choice for solitary, non-metastatic lung tumors in dogs and cats. Complete removal of the entire affected lung lobe is typically recommended. Though this procedure sounds intensive, complications are rare and most pets do very well afterwards following a brief recovery period.

Thoroscopic procedures, where specialized cameras and surgical instruments are inserted through ports located within tiny incisions into the chest, are less invasive, and useful for removing smaller tumors. At the time of surgery, any visible lymph nodes should also be biopsied to determine stage of disease.

Once the tumor is removed it is submitted for histopathology and biopsy. This will provide information as to the exact cell of origin of the tumor, as there are many different potential primary lung cancers.

Most information regarding prognosis for animals with pulmonary tumors is derived from the behavior tumors of epithelial cell origins, otherwise known as carcinoma tumors. Typical expected survival time is about one year after surgery. 

Prognostic factors are characteristics of the patient or their tumor that can influence the outcome (usually measured as survival time) in either a positive or negative way.

Prognostic factors for dogs with pulmonary tumors including stage of disease, the presence of adverse (i.e., unfavorable) clinical signs prior to diagnosis, size of the primary tumor, location of the primary tumor within the lung, and histological grade of the tumor, which is based off of features the pathologist will evaluate under the microscope.

Chemotherapy plays a large role in treating lung cancers in people. Based on this information, there are many theoretical advantages to chemotherapy’s use in pets. However, because the tumors are so rare, studies are lacking regarding proving its benefit for dogs and cats.

I recommend treatment with a drug called vinorelbine. This is an injectable form of chemotherapy shown to provide a partial response to treatment in a very small number of dogs with lung tumors. Metronomic chemotherapy is also a reasonable, theoretical treatment option.

The role of other typical treatments used in people with lung cancer, including radiation therapy, interventional radiology, and regional chemotherapy remains relatively unexplored for veterinary patients.

Because lung cancer is so common in humans, many people are aware of how serious a diagnosis it is. Though there are many shared characteristics in the disease between animals and people, it’s important to keep in mind that in both cases, though not curable, it is often a very treatable type of cancer.

If you’re facing a diagnosis of lung cancer in your dog or cat, please seek consultation with a veterinary oncologist who can provide you with all the information you need to make the right decision for your pet.

Dr. Joanne Intile