Pulmonary Neoplasia

Classification

Although metastatic pulmonary tumours are common in the lung, primary pulmonary tumours are relatively rare in domestic animals (cf. humans)
However, primary tumours are more common in dogs and cats than in other animals

Classification of pulmonary tumours can be difficult due to the metaplasia which can occur in both inflammation and in neoplasia
- Bronchial papilloma
- Bronchial adenoma/ carcinoma (arising from major airways)
- Bronchioloalveolar adenoma/ carcinoma (arising from small airways or alveolar parenchyma - either secretory bronchiolar cells or type II epithelial cells)
- Carcinoid: in humans, these tumours arise from neuroendocrine cells - rare in animals

Pulmonary carcinoma and emphysema (Image sourced from Bristol Biomed Image Archive with permission)

Adenomatosis (Image sourced from Bristol Biomed Image Archive with permission)

Alveolar cell carcinoma (Image sourced from Bristol Biomed Image Archive with permission)

In dogs usually invasive bronchogenic carcinomas mostly arising from hilar region an metastasise via the airways to other parts of the lungs
Types:
- Squamous cell - large cells with vesicular nuclei
- Adenocarcinoma - invasive and destructive, least malignant
- Adenosquamous carcinoma - both squamous and glandular part in one tumour, common, similar to metastatic
- Undifferentiated - very rare in animals
Large, irregular, pale, not well defined border
Spread through pulmonary lymphatics

Most common in dogs
Arise from either secretory bronchiolar or alveolar type II epithelial cells, often both types in same tumour
May be an incidental necropsy finding
Often occur as solitary nodules at the periphery of the lung, occasionally multiple
Histologically:
- Regular alveolar pattern
May resemble chronic inflammation or rapid metastatic spread of tumour from a primary elsewhere in the body

Also called myoblastomas
Mesenchymal origin
Occurs in horses
Grossly:
- Multiple discrete of partially confluent nodules
- Tend to be associated with major bronchi
- May cause obstruction
Histologically:
- Large polyhedral cells aggregation
- Fibrovascular stroma

Occurs in dogs
Histologically:
- Mixed, atypical lymphoreticular cells infiltrating one or more lung lobes
- Tend to invade blood vessel walls and airways
- Fibrous stroma
- Many mitotic figures

Lung carcinoma in a dog (Image sourced from Bristol Biomed Image Archive with permission)

Metastatic fibrosarcoma in canine lung (Image sourced from Bristol Biomed Image Archive with permission)

Metastatic sweat gland carcinoma in feline lung (Image sourced from Bristol Biomed Image Archive with permission)

All are malignant by definition
Relatively common in domestic species
Examples of common metastatic tumours include :
- Mammary carcinoma (dog and cat)
- Haemangiosarcomas
- Osteosarcomas
- Uterine adenocarcinoma (cattle)
- Malignant melanoma (horse)
Often manifest as multiple nodules scattered throughout the parenchyma - these lesions are often referred to as "cannon-ball" metastases, in all lung lobes
Histological examination usually shows the metastases to resemble the primary tumour however they may be either better or less well differentiated
Sometimes the metastasis can be sen only microscopically, grossly the lungs are discoloured and more firm than usual
Disseminate widely through lymphatics

In horses
- cranial mediastinal lymphosarcoma
- pulmonary granular cell tumour
- malignant melanoma
- haemangiosarcoma
- metastatic adenocarcinoma
- metastatic carcinoma

A space occupying lesion in the canine lung may produce periosteal thickening of the long bone - Hypertrophic Osteopathy