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Non-small cell lung cancer
There are two main types of lung cancer: small-cell lung cancer (sclc) and non-small-cell lung cancer (nsclc).
Lung cancer is a malignant tumour that grows in the lung or the tissues around it. It can affect the body cells lining...
Small cell - one in five lung cancer patients have this type.
Non-small cell - most other patients have one of three types of non-small cell cancer. Doctors tend to group them together because they are quite similar to each other.
Small cell and non-small cell cancers grow in different ways, and so need different treatments.
Non–small cell lung cancer (NSCLC) accounts for approximately 75% of all lung cancers. NSCLC is divided further into adenocarcinoma, squamous cell carcinoma, and large cell carcinoma. All share similar treatment approaches and prognoses but have distinct histologic and clinical characteristics.
Recently, advanced molecular techniques have identified amplification of oncogenes and inactivation of tumor suppressor genes in NSCLC. The most important abnormalities detected are mutations involving the ras family of oncogenes. The ras oncogene family has 3 members: H-ras, K-ras, and N-ras. These genes encode a protein on the inner surface of the cell membrane with GTPase activity and may be involved in signal transduction.
Animal studies performed on mice suggest the involvement of ras mutations in the molecular pathogenesis of NSCLC. Studies in humans suggest that ras activation contributes to tumor progression in persons with lung cancer. The ras gene mutations occur almost exclusively in adenocarcinomas and are found in 30% of such cases. These mutations are not identified in adenocarcinomas that develop in persons who do not smoke.
The K-ras mutation appears to be an independent prognostic factor. Studies are ongoing to develop management plans according to the presence or absence of ras gene mutations.
Non-small cell lung carcinoma (NSCLC) includes squamous cell carcinoma, adenocarcinoma, and large cell carcinoma.
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.
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. The most common lung cancer in men is squamous cell carcinoma. It usually appears in the larger breathing tubes. Like other NSCLCs, squamous carcinoma is a relatively slow-growing cancer.
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.
Adenocarcinoma is the most common type of NSCLC and the most common form of lung cancer among women. The incidence of this type of lung cancer is increasing. Adenocarcinomas often appear toward the outer edges of the lungs in the mucous glands that line the airways. Like other forms of lung cancer, adenocarcinoma may spread to other parts of the body. Bronchioloalveolar adenocarcinoma (BAC), a subtype of adenocarcinoma, is found in the tiny air sacs, called alveoli, of the lungs. BAC is a slow-growing cancer.
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.
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. Large cell carcinoma occurs less often and has larger cells than other NSCLCs. It usually first appears in the smaller breathing tubes and may spread quickly. Large cell carcinoma is typically diagnosed after other types of lung cancer have been ruled out.
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