Primary lung tumors (cancer originating in the lung) are uncommon in dogs and account for less than 1% of all tumors. It is most common in older dogs, but no specific breed or sex is predisposed. They are almost always malignant (invasive with the potential to spread).

What causes this cancer in dogs?

• Although smoking is associated with most lung cancer in people; this is not true in dogs or cats. Second hand smoke can contribute to lung tumors in short-nosed dogs (it causes nasal cancer in long-nosed dogs).

What are the clinical signs?

• Clinical signs are typically vague and not specific to the respiratory tract. About 25% of dogs will show no clinical signs of illness at all. Many dogs will show signs of general malaise: tiredness and decreased appetite.
• Symptomatic dogs can have a nonproductive cough.

How can lung cancer be diagnosed?

• A thorough physical examination may revealed abnormal or muffled lung sounds
• Radiographs (x-rays) of the chest are probably the most important tool to visualize a primary lung mass in a dog. A primary lung tumor is typically located in the caudal (towards the hind end of the dog) lung lobes, however can be located in any lung lobe. There is usually only a single mass present, unless the tumor has spread.
• A CT scan can be used in lieu of or in addition to a standard x-ray (radiograph). CT scans provide greater clarity and reveal more details than regular radiographs and can detect smaller masses.
• Additional imaging (such as abdominal radiographs or an abdominal ultrasound) is recommended to evaluate other organs for metastasis (spread of the tumor).
• If the mass is big enough, and in the ideal location (close to the chest wall), an aspirate of the mass may be attempted with a small 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 the microscopic cells for evaluation (cytology). This is a fairly safe procedure, but should be done using ultrasound guidance.
• Biopsy of tissue from the lung mass is often the only definitive way to make a diagnosis of lung cancer. This requires some form of surgery, but there are many new less invasive procedures available-such as thoracoscopy and ultrasound/CT guided tru-cut biopsy.

How are primary lung tumors treated?

• Surgical excision of the tumor is the treatment of choice for canine primary lung cancer. Depending on the size and location of the mass, complete removal may not be possible, however, most tumors are at least somewhat removable. If there is evidence of widespread metastasis (spreading of the cancer in multiple locations), surgical removal is generally not an option.

Will chemotherapy be recommended?

• If surgery is not an option, chemotherapy may be used to slow the progression of disease.
• If a primary lung tumor is of a higher “grade” (more aggressive with a high chance of spreading to other locations) or has invaded into vessels or lymphatics, chemotherapy may be used to slow the rate of metastasis (spreading). A tumor grade is obtained after a biopsy or surgical removal of the tumor.

What is the prognosis?

• The average survival times for dogs with primary lung cancer is variable, and depends on many factors including spread of the primary tumor, the presence of invasion into vessels or lymphatics, the size of the tumor, and the grade of the tumor.
• Dogs with small, low-grade (well-differentiated) tumors without lymph node involvement carry a very good prognosis, and have an average survival time of 16 months or longer with surgery alone whereas dogs with high-grade (poorly differentiated) tumors with lymph node involvement have an average survival of 2 months if surgery is the only treatment.

What is on the horizon?

• The use of targeted therapies and non-steroidal anti-inflammatory drugs (NSAID) are currently being investigated in the treatment of this tumor when used in conjunction with surgery and traditional chemotherapy.