Adenocarcinoma of the lung

Adenocarcinomata tend to occur more peripherally than squamous cell carcinomata (SCC). Adenocarcinoma accounts for approximately 20% of lung tumours - though this may be increasing - and with equal incidence in both sexes. The association with smoking is less strong than for SCC.

Adenocarinoma is the most common lung tumour in non-smokers and the lung tumour most frequently associated with asbestos.

Atelectasis and emphysema are less common in adenocarcinoma as the major bronchi are usually not impaired.

Histologically, these tumours contain epithelial mucin which stains positive with mucicarmine. Four types are recognised by the WHO classification, but in practice, two types are distinguished:

• bronchial-derived - incorporating acinar, papillary, and solid - with mucin production; may occur in association with old trauma, tuberculosis and infarctions, and has been described as a 'scar cancer'
  
  
• bronchio-alveolar - which grow along pre-existing alveolar septae

There is little difference between these two groups in terms of treatment response or survival, which on account of the relatively slow growth of these tumours, tends to be more favourable than for other lung tumours.

Lung adenocarcinomas may present a diagnostic difficulty in that an apparent primary tumour may prove to be a metastasis from a tumour of the gastrointestinal tract, ovary, pancreas, kidney, thyroid, or breast.