Lung cancer (also called pulmonary neoplasia) is caused by tumors or masses made up of cancer cells within the lungs. Some tumors are benign, meaning that they do not invade and damage the surrounding cells. Other lung tumors are malignant and will damage the surrounding cells and tissues. Malignant tumors may also metastasize, or travel to other sites and organs of the body, to cause new tumors and damage to those areas.
Lung cancer in dogs and cats can be primary, meaning the tumors originate or start growing only in the lungs. Secondary lung cancer is the result of cancer elsewhere in the body, which then spread to the lungs. Primary lung cancer is uncommon in our pets as most lung cancers are from tumors spreading to other organs. In fact, if any type of cancer is discovered in a pet, x-rays are often done on the lungs because they are one of the most common places for cancers to spread to.
How Lung Cancer Affects Pets
When a pet has lung cancer, the lungs become damaged because the tumor crowds out healthy lung tissue. Malignant tumor cells can also invade and damage pulmonary/lung blood vessels and alveoli (air-containing compartments that move oxygen from the lung’s lower airways into the bloodstream). Fluid buildup from this damage, called pleural effusion, can develop around the lungs, compressing or squeezing them and preventing air from moving in and out properly.
Unlike humans, dogs and cats have two left lung lobes and four right lung lobes. Cancer can be found in one lobe, some of them, or all of them.
Symptoms of lung cancer may be subtle at first. Poor appetite and acting tired may be noticed. Sometimes a tumor or mass is somewhere else in the body, such as in the mammary tissue, the mouth, on a toe, or under the skin. As the disease goes on, symptoms may include coughing, trouble breathing, loud snore-like breathing while awake, and possibly coughing up blood.
Diagnosing Lung Cancer
If lung cancer is suspected, the veterinarian will give the pet a thorough checkup, including listening to the heart and lungs with a stethoscope and searching carefully for other tumors. Remember that even though lung cancer tumors are inside the lungs and aren’t visible to the naked eye, most lung tumors are from cancer in another part of the body. X-rays (radiographs) will be taken of the chest to see if masses are visible. Bloodwork may be done to check the pet’s internal organ function. Sometimes, x-rays of the bones or belly may be taken to see if the cancer originated somewhere else.
Ideally, samples of a lung tumor will be taken with a needle and syringe (known as an aspirate) or a biopsy instrument. Either of these approaches may require heavy sedation or anesthesia and specialized equipment. If numerous tumors are found in the lungs and the pet’s symptoms strongly suggest cancer, this last step may not be necessary for diagnosis.
If your veterinarian is not comfortable treating lung cancer or feels that their clinic does not have the right equipment, your veterinarian may refer you to a veterinary oncologist.
In certain cases of primary lung cancer, the tumor can be surgically removed. Sometimes the entire lung must be removed to prevent tumor spread. Lobe removals are risky and difficult procedures and are often performed by a specialty veterinary surgeon.
Chemotherapy and radiation are also possible options for treatment, but they are not always successful or effective.
If treatment is not an option, supportive or palliative care therapies are the next best options. These types of therapies help the pet feel as good as they can until the cancer becomes severe. Combinations of pain medications, cough suppressants, anti-inflammatory medications (e.g. steroids), and antibiotics to fight secondary infections caused by the cancer may be prescribed.
If your pet has lung cancer, discuss all treatment and therapy options with your primary care veterinarian and, if you’ve chosen to see one, a veterinary oncologist. Your veterinarian will work with the oncologist to help you decide what is best for your pet. Pets with lung cancer can become quite sick in a short period of time. They may die or require humane euthanasia in as few as two to three weeks from diagnosis. Some pets can survive longer than a few weeks, depending on tumor type and how severe the cancer is when it initially gets diagnosed, but this is not always the case.
Each case is individual, and the outcome may – or may not – depend on treatment. Your pet could do well for months with nothing but supportive care or may not do well with surgery, chemotherapy and radiation. Even oncologists cannot predict the outcome with complete accuracy. Given the uncertainty of an outcome, no decision you make about treatment can be wrong.