Medical Health Encyclopedia

Some experts believe all primary lung cancers originate from a single common malignant stem cell that, as it reproduces, can develop into any one of these cancer types in different individuals. In addition, cancers in the lung may have spread (metastasized) from other primary sites, such as the breast, thyroid, or colon.

Non-Small Cell Lung Cancers

Non-small cell lung cancers are categorized into three types: squamous cell carcinoma (also called epidermoid carcinoma), adenocarcinoma, and large cell carcinoma. These separate types are grouped together because, in early stages before the cancers have spread, they all can be treated surgically.

Squamous Cell Carcinoma. Squamous cells are formed from reserve cells, which are round cells that replace injured or damaged cells in the lining (the epithelium) of the bronchi, the major airways. Tumors formed from squamous cells are usually found in the center of the lung, either in a major lobe or in one of the main airway branches. They may grow to large sizes and form cavities in the lungs.

Click the icon to see an image of squamous cell carcinoma.

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When squamous cell cancer metastasizes, it may travel to the bone, adrenal glands, liver, small intestine, and brain.

Squamous cell carcinoma is nearly always caused by smoking and used to be the most common cancer. It still makes up between 25% and 40% of all lung cancers.

Adenocarcinoma. Adenocarcinomas usually arise from the mucus-producing cells in the lung. About two-thirds of adenocarcinomas develop in the outer regions of the lung, while one-third develops centrally. In 1965, 12% of lung cancers were adenocarcinomas. They are now estimated to account for 30% to 50% of all lung cancers and may even be the most common. It is the predominant lung cancer in women. In fact, a 2000 multicenter European study showed that nearly 34% of the women with lung cancer under investigation presented with adenocarcinoma, compared to 26.4% with squamous cell carcinoma and 22.3% with small cell lung cancer. (Adenocarcinoma is also increasing dramatically in men.)