Malignant non-small cell epithelial tumors of the lung are classified by the World Health Organization (WHO)/International Association for the Study of Lung Cancer (IASLC). There are three main subtypes of non-small cell lung cancer (NSCLC), including the following:
Small cell lung cancer (SCLC) accounts for approximately 15% of bronchogenic carcinomas.
At the time of diagnosis, approximately 30% of patients with SCLC will have tumors confined to the hemithorax of origin, the mediastinum, or the supraclavicular lymph nodes. These patients are designated as having limited-stage disease (LD). Patients with tumors that have spread beyond the supraclavicular areas are said to have extensive-stage disease (ED).
SCLC is more responsive to chemotherapy and radiation...
Most squamous cell carcinomas of the lung are located centrally, in the larger bronchi of the lung. Squamous cell carcinomas are linked more strongly with smoking than other forms of NSCLC. The incidence of squamous cell carcinoma of the lung has been decreasing in recent years.
Adenocarcinoma is now the most common histologic subtype in many countries, and subclassification of adenocarcinoma is important. One of the biggest problems with lung adenocarcinomas is the frequent histologic heterogeneity. In fact, mixtures of adenocarcinoma histologic subtypes are more common than tumors consisting purely of a single pattern of acinar, papillary, bronchioloalveolar, and solid adenocarcinoma with mucin formation.
Criteria for the diagnosis of bronchioloalveolar carcinoma have varied widely in the past. The current WHO/IASLC definition is much more restrictive than that previously used by many pathologists because it is limited to only noninvasive tumors.
If stromal, vascular, or pleural invasion are identified in an adenocarcinoma that has an extensive bronchioloalveolar carcinoma component, the classification would be an adenocarcinoma of mixed subtype with predominant bronchioloalveolar pattern and a focal acinar, solid, or papillary pattern, depending on which pattern is seen in the invasive component. However, the future of bronchioloalveolar carcinoma as a distinct clinical entity is unclear; a multidisciplinary expert panel representing the IASLC, the American Thoracic Society, and the European Respiratory Society proposed a major revision of the classification of adenocarcinomas in 2011 that entails a reclassification of what was called bronchioloalveolar carcinoma into newly defined histologic subgroups.