Lung cancer is a term given to any cancer that originates in the lungs. There are two main classifications of lung cancers: non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC). The most common type of lung cancer is NSCLC. Approximately 85 percent of all lung cancers are NSCLC.1
What is non-small cell lung cancer?
NSCLC occurs when malignant (cancer) cells form in the tissues of the lung. The major risk factor for developing NSCLC is smoking, and signs of NSCLC include a cough that doesn’t go away and shortness of breath.1
NSCLC has several sub-types, classified by the types of cells. Each type grows and spreads in different ways. The classification is determined by looking at the malignant cells under a microscope and is important because classification helps doctors choose appropriate treatment regimens, as well as determine the prognosis or projected outcome of the cancer.1
Adenocarcinoma
Adenocarcinoma is the most common NSCLC (35-40 percent of all lung cancers) and usually occurs in a peripheral location within the lung, sometimes at the site of pre-existing scars, wounds, or inflammation. Adenocarcinomas begin in the cells that line the alveoli, the air sacs in the lungs that are responsible for the gas exchange of oxygen and carbon dioxide between the lungs and the blood.1,2 Additional characteristics of adenocarcinomas further describe the pattern of the cells under the microscope:
- Acinar refers to cells in the shape of the alveoli.3
- Papillary refers to the structure of the growth.2
- Bronchioloalveolar is a subset of adenocarcinoma that arises in the outer bronchioles or alveoli of the lung.2,3
- Mucinous refers to the tumor’s ability to create mucin, the main component of mucus.3
Squamous cell carcinoma
Squamous cell carcinoma accounts for 25-30 percent of all lung cancers and is found in the central parts of the lung, such as the bronchi. Squamous cells are flat cells that are found in the lining of the airways.2,4 Squamous cell carcinomas can be further described as papillary, clear cell, small cell, or basaloid, which refer to their appearance under the microscope.1
Large cell carcinoma
Large cell carcinoma accounts for 10-15 percent of all lung cancers and appears on chest x-rays as a large peripheral mass (mass in the outer regions of the lung). Under the microscope, cells of large cell carcinomas do not look like squamous cell carcinomas or adenocarcinomas. These tumors usually have a better prognosis than SCLC and are generally treated similarly to adenocarcinomas.2,4
Other less common types of NSCLC
There are several additional, rare types of NSCLC, including:
- Adenosquamous carcinoma, which refers to a cellular structure that is partly glandular (like adenocarcinomas) and partly surface cells (like squamous cell carcinomas)
- Sarcomatoid carcinoma, which resembles a mixture of carcinomas that line the lungs and sarcomas (a different form of cancer) that arise from connective or supportive tissue
- Pleomorphic, a subtype of sarcomatoid that is noted for having many shapes
- Salivary gland carcinoma, which is named for its similarity to tumors which begin in the salivary glands 1,3
Molecular features guide treatment recommendations
The identification of the different types of lung cancers has led to the development of treatments that are targeted to the molecular differences in tumors. Targeted therapy has been shown to improve the survival of certain groups of patients with metastatic disease.1
