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Primary lung tumors are rare in dogs (majority a result of inhaled carcinogens), whereas pulmonary metastatic neoplastic involvement is common, usually mammary adenocarcinoma and anal sac adenocarcinoma. Unlike secondary metastatic neoplasms, primary pulmonary carcinomas rarely produce hypertrophic osteoarthropathy.
Pulmonary adenocarcinoma is the most common primary lung neoplasia in dogs, with secondary metastasis to regional lymph nodes and the heart common. Alveolar carcinoma and squamous cell carcinoma also occur and anaplastic large-cell carcinomas are considered rare.
These tumors are usually classified as either differentiated or undifferentiated based on histologic pattern rather than histogenesis. As metastatic rate and survival appear to vary with classification, pattern distinction is of primary prognostic importance.
Affected dogs usually present with coughing, dyspnea, inspiratory wheezing, epistaxis, fever, weight loss and anorexia. Pulmonary edema and hypertrophic osteoarthropathy have been reported in advanced cases.
Diagnosis is based on imaging with radiography, CT or MRI. Transcutaneous pulmonary biopsy, tracheobronchial washes or tracheal endoscopy are frequently employed to assist diagnosis.
Radiographically, these tumor may appear as a single mass or a nodular-disseminated growth, mimicking the metastatic involvement of the lung.
A definitive diagnosis usually requires histopathology of biopsied material.
Immunohistochemistry of biopsies usually shows negative staining for vimentin with papillary adenocarcinomas while adenocarcinomas usually stain positive for cytokeratin.
Regional mediastinal lymphadenopathy is suggestive of a poorer prognosis.
A differential diagnosis would include heartworm disease, lymphoma, cranial mediastinal carcinoma, lungworm (e.g. Filaroides osleri), bronchial carcinoma, metastatic mammary adenocarcinoma, Coccidioides spp, Aspergillus spp, Nocardia spp and Mycobacterium spp.
Treatment usually requires lobectomy via thoracotomy or endoscopy in cases where the trachea is unaffected by metastases, and is usually curative. Adjunct radiation therapy or chemotherapy may be required.
Long term remission is good for small differentiated adenocarcinomas. Undifferentiated carcinomas have over a 50% incidence of metastasis. The prognosis for squamous cell carcinoma is poor with a metastasis rate of over 90%.
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