HISTOLOGICAL PATTERN OF LUNG ADENOCARCINOMA
- Lung carcinomas are mainly divided into two groups: non small cell (NSCLC) and small cell carcinoma (SCLC)
- Adenocarcinoma is a type of NSCLC arising from the bronchi, bronchioles and alveolar cells, with or without mucin production.
- In 2011, the International Association for the Study of Lung Cancer, American Thoracic Society, and European Respiratory Society revised the classification of lung adenocarcinoma and proposed new morphological criteria to provide a uniform diagnostic terminology for multidisciplinary patient management.
- Different histologic subtypes in lung adenocarcinomas include lepidic, acinar, papillary, micropapillary, and solid subtypes:
Lepidic pattern is defined as a tumor composed of neoplastic cells lining the alveolar lining with no architectural disruption/complexity, and no lymphovascular and/or pleural invasion
Acinar pattern is characterized by glandular formation
Papillary pattern displays true fibrovascular cores lined by tumor cells replacing the alveolar lining
Psammoma bodies may be present .
Micropapillary is composed of ill-defined projection/tufting with no fibrovascular cores
Solid pattern is defined as solid sheets and nests of tumor
- Most lung adenocarcinomas demonstrate a mixture of different histologic patterns
- Different histologic subtypes have prognostic significance, with lepidic subtype harboring the best course, and micropapillary and solid patterns having a more aggressive behavior
- Based on this classification, adenocarcinomas measuring 3 cm or less in greatest dimension and pure lepidic pattern with no features of invasion are classified as “adenocarcinoma in-situ”.