| Primary lung tumors are rare in dogs and cats; however, the reported incidence of lung carcinomas has increased at least 100% during the last 20 yr. This is attributed to an increased average life span, better detection and awareness, or, possibly, increasing exposure to environmental carcinogens. Most primary lung tumors are diagnosed at a mean age of 10-12 yr in dogs and 12 yr in cats. There is no consistent breed or sex predilection in either species. Primary lung tumors usually
originate from the terminal bronchioles and alveoli; they occasionally occur as a second coincidental tumor, which may make the differentiation between primary and metastatic disease difficult. Of the primary lung tumors in dogs and cats, ≥80% are malignant. Adenocarcinoma and anaplastic carcinoma are the most common types in dogs and cats. Primary lung sarcomas and adenomas are rare in both species. Metastatic spread of primary lung tumors is generally to other areas of the lungs,
tracheobronchial lymph nodes, bone, and brain. Intrapulmonary spread via the airways occurs in ~50% of dogs with adenocarcinoma. Metastatic spread to the pleurae, pericardium, heart, and diaphragm may occur; miscellaneous extrathoracic sites include liver, spleen, and kidney. Dogs with papillary (bronchoalveolar) adenocarcinoma have a better prognosis than those with other lung tumors; however, histologic grade and detection of clinical signs are the most important determinants of
prognosis and survival. Both recurrence and metastasis tend to occur earlier and with greater frequency in dogs with moderately or poorly differentiated tumors. |
| Clinical Findings: |
| Primary lung tumors have variable manifestations, which depend on the location of tumor, rapidity of tumor growth, presence of previous or concurrent pulmonary disease, and awareness of the owner. Common signs include cough, inappetence, weight loss, reduced exercise tolerance, lethargy, tachypnea, dyspnea, wheezing, vomiting or regurgitation, pyrexia, and lameness. The most common clinical finding in dogs is a chronic, nonproductive cough. Coughing is uncommon in cats;
nonspecific signs, such as inappetence, weight loss, and tachypnea and dyspnea, are more common. In either species, tachypnea or dyspnea indicates massive tumor burden or pleural effusion. Pleural effusion is particularly common in cats with primary lung tumors. Lameness may be due to hypertrophic osteopathy (unusual in cats) or to metastasis to bone or skeletal muscle. Thoracic auscultation may be normal, reflect increased breath sounds compatible with pulmonary airway disease,
or be muffled due to pulmonary consolidation or pleural effusion. |
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| Diagnosis: |
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One-third or more of primary lung tumors are recognized incidentally during radiography for other problems, or at necropsy. Thoracic radiographs are essential for a tentative diagnosis in those animals exhibiting compatible clinical signs. Primary lung tumors in dogs may occur as single or multiple circumscribed mass lesions, as a diffuse lung pattern, or as a lobar consolidation. In cats, single circumscribed mass lesions are less common,
whereas a diffuse lung pattern or lobar consolidation is more frequent. Pleural fluid accumulation is common in cats and less frequent in dogs. In either species, chest wall involvement and hilar lymphadenopathy may be seen. Tentative diagnosis can be made by ruling out other causes of pulmonary disease with similar radiographic lung patterns. Definitive diagnosis requires biopsy. |
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| Treatment: |
| Surgical resection of tumor via lobectomy of diseased lung lobes is the treatment of choice. Inoperable lesions or metastatic disease may be controlled with chemotherapy. Mean survival time for operable solitary, well-differentiated, primary lung tumors without node involvement in dogs is 15-26 mo; if the lymph nodes are involved or multiple tumors are found at the time of diagnosis, survival time is shortened. Recurrence or metastasis of tumor is a common cause of death. |
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