Canine Lung Cancer
Primary lung tumors are relatively uncommon in dogs and account for only 1% of all tumors in this species. There has been a potential association with dogs developing lung tumors in a household of people who smoke as a result of second-hand smoke inhalation. The most common history of dogs with lung tumors is to present with coughing or exercise intolerance that may have been present for a relatively long time. Sometimes dogs have no clinical signs and the tumor is simply noted on routine radiographs.
Tumors are definitively diagnosed through a fine needle aspirate or through biopsy, which often involves removal of a lung lobe. The most common types of lung tumors are adenocarcinomas (bronchogenic or alveolar). Other types include squamous cell carcinoma, anaplastic and undifferentiated carcinoma, and rarely a sarcoma. These tumors can spread to nearby lymph nodes and then to other lung lobes or spread via the creation of a malignant pleural effusion (fluid in the chest with cancer cells noted in it). Rarely this type of cancer can cause lameness and swelling of legs due to inflammation of the bones caused by cancer in the chest. Routine blood work is always performed but not usually diagnostic for the cancer itself.
Treatment is via surgical removal of the affected lung lobe. At that time, any lymph nodes in the area are examined and aspirated if needed. Chemotherapy is often used when dogs have any poor prognostic indicators and if the cancer appears to have spread, or residual cancer is left in the chest. Many chemotherapy agents have been used, however, to date, no specific studies on which protocol is best is available. Generally, when chemotherapy is used the protocol depends upon the clinician’s experience. Recently, similar protocols to those used in human oncology have been used these include the use of Carboplatin and Vinorelbine. Additionally, there has been a great deal of interest in the use of nonsteroidal anti-inflammatory agents (NSAIDs) that have been shown to have anticancer effects against a variety of tumors in dogs.
Prognosis is dependent upon the presence of several indicators including:
1. Size (< 2 inches is good)
2. Metastasis (poor)
3. Malignant effusion (poor)
4. Tumor adhered to the chest wall (poor)
5. Squamous cell carcinoma (poor)
6. Undifferentiated tumors (poor)
7. Tumor in the periphery (good) vs central (poor)
8. Clinical signs at presentation (poor)
9. High-grade tumor (poor) vs low grade (good)
Generally, studies have shown that the overall survival time is greater than a year. Dogs with mostly good prognostic factors typically survive 1.5 years or longer, whereas those with negative prognostic factors have an average survival time of 6-10 months.