An update on diagnosing and treating primary lung tumors - Veterinary Medicine
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An update on diagnosing and treating primary lung tumors
The incidence of this rare cancer in dogs and cats may be on the rise. Find out how to spot a primary lung tumor and what new forms of therapy may soon be at your disposal.


Computed tomography

The correlation between tracheobronchial lymph node involvement and shorter remission times stresses the importance of computed tomography (CT) in the diagnostic work-up of dogs with primary lung tumors.2,3,7 In a study of 14 dogs with primary lung tumors, researchers evaluated the accuracy of CT vs. thoracic radiography in determining tracheobronchial lymph node involvement. CT had greater sensitivity and an increased predictive value for detecting tracheobronchial lymph node metastasis. The overall accuracy of CT in detecting lymph node metastasis was 93% compared with 57% for thoracic radiographs. False negative diagnoses made with thoracic radiographs may be attributable to the fact that the lymph nodes were still small (< 15 mm) or may have been obscured by surrounding structures, including the primary tumor itself.7

5. A thoracic computed tomographic image from a 12-year-old castrated male domestic shorthaired cat presented for evaluation of inappetence and weight loss. A cavitated mass (arrows) is identified in the periphery of the right caudal lung lobe. The mass was removed with thoracoscopic lung lobectomy, and the histologic examination results revealed a well-differentiated adenocarcinoma. (Photograph courtesy of Dr. Kristen O Dell-Anderson.)
The sensitivity of CT is also superior in imaging metastatic pulmonary nodules when compared with thoracic radiography. CT was found to detect not only smaller pulmonary nodules (1 mm, compared with the minimum nodule size of 7 to 9 mm detectable on radiographs) but also a greater number of total nodules at more precise lobar locations (Figure 5). Radiographs failed to detect 90% of nodules detected on CT.39 These recent studies suggest that thoracic CT is rapidly becoming a mandatory diagnostic test performed before surgical removal of any primary tumor with potential pulmonary metastasis.


The presence of metastasis greatly affects prognosis, and appropriate clinical staging involves thoroughly investigating the common sites of pulmonary tumor dissemination. Pulmonary carcinomas tend to invade locally and spread through the lymphatic system to additional lung sites, hilar lymph nodes, and other thoracic tissues.2,3,5,12,15,16 Multiple tumor masses within the lung may indicate intrapulmonary metastasis or multicentric primary lung tumors.6 In addition to neighboring lung tissue, additional sites of metastasis include other lymph nodes, abdominal viscera, and the kidneys.12 Less common sites include the uvea, brain, and adrenal gland.40

In dogs, the rate of metastasis correlates well with the histologic type of tumor. The reported rate of metastasis is 50% for adenocarcinoma, with the most common sites of metastases being the tracheobronchial lymph nodes or other sites within the thoracic cavity.2,3,12,15 The metastatic rate is 90% for the more aggressive squamous cell carcinomas and anaplastic carcinomas.12


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