Lung cancer takes years to develop. After exposure to carcinogens, a few unusual cells begin to develop. With continued exposure, more abnormal cells appear. These cells may be on their way to becoming cancerous and forming a tumor. Lung tumors almost always start in the spongy, pinkish gray walls of the bronchi — the tubular, branching airways of the lungs. More than 20 types of malignant tumors that originate in the lung itself — primary lung cancer — have been identified. The major types are small-cell lung cancer and non-small cell lung cancer. The more common non-small variety is divided into:
- Adenocarcinoma — the most common type of lung cancer — tends to originate along the outer edges of the lungs in the small bronchi or smaller bronchioles. Adenocarcinoma often spreads to spaces between the lungs and the chest wall, and its typical location makes early detection difficult. Adenocarcinoma often presents as a metastasis (site of cancer spread) in the brain or in a bone, before the patient has any symptoms in the chest.
- Squamous cell carcinoma usually starts in cells of the central bronchi, the largest branches of the bronchial tree. It is the easiest to detect early, since its distinctive cells are likely to show up in tests of sputum samples. It also tends to be most curable if found early because it spreads relatively slowly.
- Large-cell carcinomas are a group of cancers with large, abnormal-looking cells that tend to originate along the outer edges of the lungs. They are the least common of the non-small-cell lung cancers.
Small-cell lung cancer is the most aggressive form of the disease; it is also called oat-cell cancer because, under a microscope, its cells resemble oat grains. Like squamous cell carcinoma, this cancer usually originates in the central bronchi. It spreads quickly, often before symptoms appear, making it particularly threatening. It frequently spreads (metastasizes) to the liver, bone and brain. Although responsive to chemotherapy, small cell lung cancer is less frequently cured because it usually is not discovered before it has spread.
Copyright 2003 National Women's Health Resource Center Inc. (NWHRC)