Lung Cancer (Classification, Non-Small-Cell Lung Carcinoma)

Classification

Lung cancers are classified according to histological type. This classification has important implications for clinical management and prognosis of the disease. The vast majority of lung cancers are carcinomas—malignancies that arise from epithelial cells. The two most prevalent histological types of lung carcinoma, categorized by the size and appearance of the malignant cells seen by a histopathologist under a microscope: non-small-cell and small-cell lung carcinoma. The non-small-cell type is the most prevalent by far (see accompanying table).

Cancer found outside of the lung may be determined to have arisen within the lung, as lung cancers that metastasize, i.e. spread, often retain a cell marker profile that allow a pathologist to say, with a good deal of certainty, that the tumor arose from the lung, i.e. is a primary lung cancer. Primary lung cancers of adenocarcinoma histology typically have nuclear immunostaining with TTF-1.

Frequency of histological types of lung cancer

Histological type	Frequency (%)
Non-small-cell lung carcinoma	80.4
Small-cell lung carcinoma	16.8
Carcinoid	0.8
Sarcoma	0.1
Unspecified lung cancer	1.9

Non-small-cell lung carcinoma

The non-small-cell lung carcinomas (NSCLC) are grouped together because their prognosis and management are similar. There are three main sub-types: squamous cell lung carcinoma, adenocarcinoma, and large-cell lung carcinoma.

Accounting for 25% of lung cancers, squamous cell lung carcinoma usually starts near a central bronchus. A hollow cavity and associated necrosis are commonly found at the center of the tumor. Well-differentiated squamous cell lung cancers often grow more slowly than other cancer types.

Adenocarcinoma accounts for 40% of non-small-cell lung cancers. It usually originates in peripheral lung tissue. Most cases of adenocarcinoma are associated with smoking; however, among people who have never smoked ("never-smokers"), adenocarcinoma is the most common form of lung cancer. A subtype of adenocarcinoma, the bronchioloalveolar carcinoma, is more common in female never-smokers, and may have different responses to treatment.

Sub-types of non-small-cell lung cancer in smokers and never-smokers

Histological sub-type		Frequency of non-small-cell lung cancers (%)
		Smokers	Never-smokers
Squamous cell lung carcinoma		42	33
Adenocarcinoma	Adenocarcinoma (not otherwise specified)	39	35
	Bronchioloalveolar carcinoma	4	10
Carcinoid		7	16
Other		8	6