Primary Lung Tumor

In dogs and cats, tumors found within the lung lobes are most commonly the result of metastasis, meaning cancer cells have traveled through the bloodstream from another primary site and lodged in the lungs. Tumors that originate directly from lung tissue (primary lung tumors) are considerably less frequent.

Most primary lung tumors arise from glandular tissue and are classified as adenocarcinomas or bronchogenic carcinomas. Less commonly, they may develop from the supportive structures of the lung, including:

• fibrosarcomas (from fibrous tissue),
• chondrosarcomas (from cartilage),
• hemangiosarcomas (from blood vessels),
• or other mesenchymal tissues.

Exposure to environmental risk factors increases the likelihood of primary lung tumors. Dogs and cats living with smokers or in polluted environments, including those with asbestos exposure, are at higher risk. Brachycephalic breeds (e.g. bulldogs, pugs) are more susceptible than long-nosed breeds.

Primary lung tumors are typically diagnosed in middle-aged to older dogs and cats. Approximately 25% of affected animals show no clinical signs, and tumors may be detected incidentally during chest radiographs taken for unrelated reasons.

When present, clinical signs may include:

• coughing,
• weight loss,
• lethargy.

Large tumors or those compressing critical structures may cause respiratory distress or regurgitation, characterized by passive return of food shortly after eating. Some animals develop lameness due to metastatic spread or as a result of hypertrophic osteopathy, a condition involving swelling and abnormal bone formation in the distal limbs.

Pulmonary tumors are identified using thoracic radiographs or computed tomography (CT) of the chest. On standard x-rays, lung tumors are typically not visible until they reach a diameter of approximately 1.3 cm (½ inch).

Tumors that are large or located near the chest wall may be sampled via fine-needle aspiration, with cytologic examination used to determine tumor type. Because affected animals are often older, routine blood and urine testing is performed to evaluate for concurrent disease. Additional staging tests, such as abdominal ultrasound, may be recommended to identify a primary tumor elsewhere in the body.

When a single lung lobe tumor is present, surgical removal is the treatment of choice. This can be performed via a traditional open approach using a thoracotomy or through minimally invasive thoracoscopic techniques.

Animals with multiple lung lobe tumors most commonly have metastatic disease, in which case systemic treatments such as chemotherapy may be considered instead of surgery.

Dogs and cats have multiple lung lobes that can be removed individually. Most lung lobectomies are performed through a thoracotomy, involving an incision between the ribs just behind the front limb. The blood vessels and bronchus supplying the affected lobe are sealed using sutures or surgical staplers, with staplers commonly preferred due to speed and reliability.

A chest tube is placed postoperatively to evacuate air or fluid from the chest cavity and may also be used to deliver local anesthetics for pain control. Chest tubes are typically removed within 12–24 hours. Pain management often includes a combination of:

• epidural anesthesia,
• intravenous analgesics,
• transdermal fentanyl patches,
• and oral medications once the pet is awake.

Following surgery, pets remain hospitalized until the chest tube is removed, breathing is stable, and pain is controlled with oral medications. Physical activity is restricted for 10–14 days. Some animals may require bandaging or an Elizabethan collar to protect the incision.

Depending on histopathologic findings, chemotherapy may be recommended. Follow-up chest imaging is often advised to monitor for recurrence or metastasis.

General anesthesia carries increased risk in older patients, particularly those with compromised airways. Some animals require mechanical ventilation during surgery. Potential complications include bleeding, air leakage, and postoperative pain that can limit lung expansion and oxygenation. Despite these risks, the majority of dogs and cats recover successfully.

Temporary difficulty with walking and localized swelling near the incision are common for up to two weeks, especially due to the proximity of the incision to the front limb.

Average survival following lung lobectomy for primary lung tumors is one year or longer. Prognosis is improved when tumors are small, peripherally located, completely excised, and when lymph nodes are not involved. Reported survival times include:

• 15–17.5 months for peripheral tumors,
• ~20 months when lymph nodes are normal,
• ~19 months for completely excised adenocarcinomas,
• ~8 months for squamous cell carcinomas.

The most favorable prognosis is seen in animals with small, well-differentiated papillary carcinomas diagnosed before clinical signs and without lymph node metastasis. Cats more commonly present with metastatic disease, resulting in a poorer prognosis compared to dogs.

Avoidance of second-hand smoke is the most effective preventive measure. Even when smoking occurs outdoors, carcinogens can be transferred indoors via clothing and hair.