- Bronchogenic (columnar cell) carcinomas, including adenocarcinomas and squamous cell carcinomas.
- Bronchoalveolar (cuboidal cell) carcinomas, which may be present as multiple nodules arising from multicentric sources.
Secondary (metastatic spread)
- Primary lung tumours can metastasise within the lung itself by lymphogenous and haematogenous routes or by transmigration of cells across alveoli and bronchi.
- The lung is a major site for metastases from neoplasia in other organs, and metastatic spread from neoplasms is often the prime reason for euthanasia in cancer patients.
- The major carcinomas metastasising to the lung include mammary and thyroidal adenocarcinomas, tonsillar and digital cell squamous carcinoma, digital melanoma, lymphosarcoma and osteosarcoma.
- Multicentric neoplasms, such as lymphoma and mastocytoma, may have the lung as one of the tumour sites.
- Neoplasia of the larynx and trachea is rare.
- CLINICAL SIGNS
- The clinical findings with pulmonary neoplasia can be variable but are also progressive. The clinical signs are related to the extent of the neoplastic changes and the location of tumour masses ( Table 19.4 ).
- Pulmonary neoplasms are primarily conditions of middle- to old-aged animals with very few reports in dogs under 7 years of age, although lymphoreticular neoplasm of the lung has been reported in young dogs.
- The onset and progression of clinical signs tend to appear over a period of weeks and there is slow progressive deterioration over the subsequent weeks or months. However, rapid onset of clinical signs over several days can occur.
- Coughing is a reasonably consistent finding in cases of primary neoplasia where the tumour mass is compressing larger airways. The cough is usually soft and non-productive. With secondary neoplasms, respiratory distress rather than coughing may be the main presenting sign.
- Exercise intolerance develops because of the loss of functional lung tissue or compression of larger airways by the tumour. Pain associated with the neoplasm may also restrict exercise ability.
- Tachypnoea appears in order to maintain minute volume. The presence of tachypnoea at rest is indicative of extensive lung damage and is a grave prognostic sign.
- Expiratory dyspnoea is caused by airway compression by single solitary neoplasms and can impede emptying of a section of lung during expiration. This results in air trapping resulting in an additional expiratory effort, often heard as an end-expiratory 'grunt'.
- Haemoptysis may occur, although dogs and cats rarely expectorate sputum. Blood is often found with pulmonary neoplasms on bronchoscopy and is due to vessel erosion and microvascular leakage.
- Hypertrophic pulmonary osteopathy (Marie's disease) results in lameness due to bilateral, symmetrical and painful soft tissue swellings overlying the periosteum of the distal long bones. This condition is occasionally seen with thoracic neoplastic and non-neoplastic masses, even before the thoracic masses are visible on radiographs.
- Additional non-specific signs of systemic illness, such as pyrexia, anorexia, cachexia and general lethargy, can be found with pulmonary neoplasia.
- Gastrointestinal signs may be present, particularly in cats, with dysphagia, regurgitation or vomiting.
- Secondary bronchopneumonia can occur due to proliferation of bacteria in the airways in response to the general inflammatory process and the partial or complete blockage of airflow through a large airway by the tumour mass.
- Pneumothorax can result from airway wall erosion or rupture, although this is a reasonably rare finding.
- PULMONARY NEOPLASIA: DIAGNOSIS/Bronchoscopy
- The common findings are dynamic compression of larger airways and the presence of blood-tinged mucus in the airway ( Plate 12 ), and the demonstration of neoplastic cells in bronchial samples is diagnostic, There may be no detectable abnormalities in some cases or alternatively there may be airway inflammation, with secondary bacterial infections and a predominantly neutrophil-rich inflammatory exudate.
- PULMONARY NEOPLASIA: Therapy
- The delay in the diagnosis of most cases of pulmonary neoplasia in dogs and cats makes therapy difficult and often unrewarding ( Plate 13 ). Surgical removal of operable masses and palliative medical therapy can be used to give temporary relief.
- Lung lobectomy or pneumonectomy can be used for primary or solitary secondary neoplasms and might be curative for some slow-growing carcinomas. Where there are multiple nodules, surgery is not usually recommended.
- Medical control with radiation therapy, chemotherapy and immunotherapy is
- rarely undertaken. Chemotherapy is usually ineffective for primary tumours, but may be of some use in secondary neoplasia, although the prognosis is still grave. Chemotherapeutic regimes can be found in suitable textbooks.
- Little data are available on the benefits of radiotherapy in pulmonary neoplasia.
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