Lung cancer originates in the epithelial cells that line the airways of the lungs.
Lung cancer type depends on the type of cell from which the cancer originates, which can be observed using microscopy. The different types include:
- Small cell lung cancer or SCLC
- Non-small cell lung cancer or NSCLC
- Other types of lung cancer
In the United States, 20% of lung cancers are SCLC and nearly 80% are NSCLC. Both these cancers differ in their rate and pattern of growth as well as in their potential to spread to other organs. They are also treated differently. The classification is based on the 1999 World Health Organization and the International Association for the Study of Lung Cancer systems.
Small Cell Lung Cancer
This type of cancer is characterized by abnormally small cancer cells. The cells have an oat grains appearance under the microscope and this type of cancer is also known of as oat cell carcinoma. SCLC is also sometimes called small cell undifferentiated carcinoma.
SCLC is most commonly seen in smokers, with only about 1% of cases occurring in non-smokers. These are quickly growing tumors affecting the larger airways and they can spread to the lymph nodes and other organs. SCLC initially responds to chemotherapy and radiation therapy.
Non-Small Cell Lung Cancer
This type of cancer is further divided into the following subtypes:
- Squamous cell carcinoma
- Large cell carcinoma
Each of these subtypes have a growth pattern that differs from that of SCLC.
Adenocarcinoma originates in the glands and most of the tumors produce thick mucin. There are several types of adenocarcinoma including acinar adenocarcinoma, papillary adenocarcinoma and bronchioloalveolar adenocarcinoma. Adenocarcinoma involves the smaller airways and leads to the scarring of lung tissue. Adenocarcinomas are seen in 40% of all lung cancer cases in the United States and are more common among women and non smokers.
Squamous cell carcinoma (SCC), also called epidermoid carcinoma, is more common among men and among smokers. These tumors produce keratin, which can be seen under the microscope. SCC affects the larger airways and forms around 25% to 30% of lung cancers in the United States. The subtypes include papillary SCC, clear cell SCC, small cell SCC, and basaloid SCC.
Large cell carcinoma accounts for around 10% to 15% of all lung cancer. It can be found in any part of the lung and tends to grow and metastasize very quickly, making it more difficult to treat. Subtypes of this cancer include clear cell carcinoma, basaloid carcinoma, lymphoepithelioma-like carcinoma and large cell neuroendocrine carcinoma.
Other types of lung cancer
These include carcinoid tumors, fibrosarcomas, malignant pleural mesotheliomas and leiomyosarcomas.