There are two major categories of lung cancer: small cell and non-small cell. Small cell lung cancers are usually found in smokers, include small cell carcinoma and combined small cell carcinoma, and account for only about 15 percent of lung cancers, according to the American Cancer Society (ACS). Non-small cell lung cancer includes squamous cell carcinoma, adenocarcinoma and large cell carcinoma, and accounts for approximately 85 to 90 percent of lung cancers. The distinction between these two groups is made by how the cancer cells appear microscopically.
Small Cell Lung Cancer
Small cell carcinoma and combined small cell carcinoma are sub-types of small cell lung cancer, or SCLC. According to the National Cancer Institute (NCI), microscopic examination of the affected cells reveals irregular borders, high numbers of mitochondria and possibly absent nucleoli. This disease may also be known as "oat cell" cancer or carcinoma. SCLC is normally caused by smoking, and begins in the bronchi of the lungs.
Squamous Cell Carcinoma
Squamous cell carcinoma is a sub-type of non-small cell lung cancer, or NSCLC. The ACS says this sub-type accounts for 25 to 30 percent of all occurring lung cancers. Smoking is a common risk factor among patients with this cancer, which also begins in the bronchi of the lungs.
Adenocarcinoma
This sub-type of NSCLC accounts for nearly 40 percent of all lung cancers. Furthermore, patients suffering from the specific adenocarcinoma, known as bronchioloalveolar carcinoma, are expected to have a more positive prognosis. This type of cancer generally develops after the precursor of a lesion or other morphological changes in the lung tissue, says the NCI.
Large-Cell (Undifferentiated) Carcinoma
This type of NSCLC is responsible for approximately 10 to 15 percent of all lung cancers. It is not specific to any one area of the lung, and is very difficult to treat because it is known to spread rapidly.
Carcinoid Tumors
In addition to SCLC and NSCLC, less common carcinoid tumors can account for up to 5 percent of all lung cancers. These include typical carcinoid tumors and atypical carcinoid tumors, which have more positive prognoses than SCLC and NSCLC. Surgical removal is typically the most common treatment for these tumors.
