Lung Tumors

By Christopher Pinard, DVM

Tumors, Pet Services

What is a lung (pulmonary) tumor?

A lung (pulmonary) tumor is a type of cancer that develops from the disorganized uncontrolled production of epithelial cells (a type of skin cell) found within the lungs. The most common type of tumor of the lungs is a pulmonary carcinoma. Other types of tumors can develop in the lungs, but these are the result of metastasis (spread) from a tumor elsewhere in the body, and are not considered to be primary lung tumors.

Primary pulmonary tumors are rare in both dogs and cats.

What causes this type of cancer?

The reason why a particular pet may develop this, or any, cancer is not straightforward. Very few cancers have a single known cause. Most seem to be caused by a complex mix of risk factors, some environmental and some genetic or hereditary. Certain breeds are particularly predisposed to developing pulmonary carcinomas, including Boxer Dogs, Doberman Pinschers, Australian Shepherds, Irish Setters, Bernese Mountain Dogs, and Persian Cats. As with people, exposure to cigarette smoke has also been linked to the development of lung tumors.

What are the clinical signs of lung cancer?

The clinical signs of lung cancer can vary. Only about two thirds of dogs and cats actually exhibit clinical signs. Those that do may have difficulty breathing (labored or rapid breathing, even while resting), reduced ability to manage walks (exercise intolerance), decreased appetite, weight loss, coughing or sneezing (with or without discharge or blood), lethargy, and lameness.

"Only about two thirds of dogs and cats actually exhibit clinical signs."

Some pets develop symptoms that occur at sites distant from the tumor or its metastasis, called paraneoplastic syndrome. Paraneoplastic syndromes can affect many different body systems. The signs may include fever, weakness (with low red cell count and/or blood glucose), skin rashes and sores, hair loss, gastrointestinal ulcers, and drinking and urinating much more than normal (with high blood calcium). Lameness may develop related to excessive bony production (called hypertrophic osteopathy).

In cats, a specific syndrome called lung-digit syndrome can occur. This is the result of metastasis (spread) from the pulmonary carcinoma to the toe(s) (digits) causing swelling, pain, and lameness. See handout “Squamous Cell Carcinoma in Cats” for information on lung-digit syndrome.

How are lung tumors diagnosed?

This type of tumor is often diagnosed incidentally through chest X-rays in older (senior or geriatric) pets. Diagnosis can be confirmed through ultrasound-guided fine needle aspiration (FNA). FNA involves taking a small needle with a syringe and suctioning a sample of cells directly from the tumor and placing them on a slide. A veterinary pathologist then examines the slide under a microscope.

These samples are not always valuable for diagnosis and instead a biopsy (surgical excision of a piece of the tumor) is required. Pieces of the tumor are then examined under the microscope. This is called histopathology.

How does this cancer typically progress?

Pulmonary tumors have a high potential to spread elsewhere in the body. Metastasis within the lung tissue or local lymph nodes in both cats and dogs is quite common. About 70% of dogs will have metastasis to other lobes of the lung or lymph nodes, while 20% will have additional spread to other parts of the body. Anywhere from 50-90% of cats will have metastasis of some form.

"Pulmonary tumors have a high potential to spread elsewhere in the body."

Given that metastasis is common, routine staging (searching for potential spread to other locations in the body) is highly recommended. This may include bloodwork, urinalysis, repeat X-rays or CT scan of the lungs, and possibly an abdominal ultrasound. CT scans provide detail as to how invasive the tumor is and its exact location, as well as detail regarding lymph node involvement or indications of spread to other areas of the body.

In some cases, fluid can develop in or around the lungs, called pleural effusion. If your pet is diagnosed with pleural effusion, your veterinarian may recommend placing a needle and removing the fluid for diagnostics, as well as symptomatic relief of your pet. The procedure to remove the fluid is called a thoracocentesis.

What are the treatments for this type of tumor?

For solitary tumors that are in only one lobe of the lung, surgery is often the treatment of choice. Your pet may be a candidate for a thoracoscopy; the medical procedure to examine the inside of the chest and biopsy or remove the tumor with the use of an endoscope. Thoracoscopy allows for a smaller incision that is less invasive. Your veterinarian will recommend the best surgical procedure for your pet. During surgery, the lymph nodes associated with the lung tissue may also be removed.

Radiation therapy may be recommended if surgery is not possible. Chemotherapy may be recommended after surgery or in combination with radiation therapy if spread has been confirmed.

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