Non-Small Cell Lung Cancer - Introduction

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.)

Until recently, adenocarcinoma was only weakly linked to smoking. Experts now suggest, however, that the dramatic increase over the past decades in this lung cancer type may be due to low-tar, filtered cigarettes. People who smoke them draw tiny particles deeper into the lungs, thereby possibly increasing the risk for adenocarcinoma.

The course of this cancer varies widely. Most often, it develops slowly and causes no or few symptoms. In some cases, however, it can be extremely aggressive and rapidly fatal. In 50% of cases when it metastasizes, it spreads only to the brain. Other locations that it favors include the other lung, the liver, the adrenal glands, and bone.

Click the icon to see an image of adenocarcinoma.

Bronchoalveolar Lung Cancer. Bronchoalveolar lung cancer is actually a subtype of adenocarcinoma. It develops as a layer of column-like cells on the lung and spreads through the airways, causing great volumes of sputum. This cancer also is increasing in incidence.

Large Cell Carcinoma. Large cell carcinoma, which makes up about 10% to 20% of lung cancers, includes cancers that cannot be identified under the microscope as squamous cell cancers or adenocarcinomas.

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

Small Cell Lung Cancer

Small cell lung cancer may, like squamous cells, be derived from reserve cells or other cells in the epithelium. It causes between 15% and 25% of all lung cancers; without chemotherapy, it is very aggressive and is usually rapidly fatal. It requires a different treatment approach from non-small cell lung cancer, so it is not discussed in this report.