Types of Lung Cancer

Lung cancers, also referred to as bronchogenic carcinomas, are mainly classified into two types:

1. Small Cell Lung Cancers (SCLC).
2. Non-Small Cell Lung Cancers (NSCLC).

This classification of lung cancers is based upon the appearance of the tumor cells under the microscope. The growth, spread and treatment of these two types of lungs cancers is different, so it is important to differentiate between these two different types of lung cancer.

These comprise of around 10% to 15% of total lung cancers. SCLC is an aggressive and rapidly growing type of lung cancer. Small Cell Lung Cancers are strongly related to cigarette smoking. Small Cell Lung Cancers metastasize very fast to multiple sites inside the body and are commonly discovered after they have spread extensively.

This is the commonest lung cancer and accounts for about 85% of all the lung cancers. There are again three main sub-types of Non-Small Cell Lung Cancers based on the type of cells present in the tumor and they are:

1. Adenocarcinomas: These are commonest type of Non-Small Cell Lung Cancers in the United States and make up for about 40% of lung cancer cases. Adenocarcinomas, just like other lung cancers, are also associated with smoking; however, adenocarcinomas can also develop in non-smokers, particularly women who develop lung cancer. Majority of the adenocarcinomas develop in the peripheral or outer regions of the lungs. Adenocarcinomas tend to spread to the lymph nodes and further. Adenocarcinoma has a subtype which is known as adenocarcinoma in situ which commonly develops at multiple locations in the lungs. Adenocarcinoma in situ metastasizes along the preexisting alveolar walls. The frequency of Adenocarcinoma in situ is increasing and women are more often affected by this cancer. Adenocarcinoma in situ can appear as pneumonia on a chest x-ray. Adenocarcinoma in situ has a better prognosis than other lung cancer types.
2. Squamous Cell Carcinomas: Previously, this type of lung cancer was more common than adenocarcinomas; however, now they comprise of around 25% to 30% of all the cases of lung cancer. Squamous Cell Carcinomas are also known as epidermoid carcinomas, and originate commonly in the central chest area in the bronchi. Squamous Cell lung Carcinomas often stays within the lung and metastasizes to the lymph nodes, grow in size and form a cavity.
3. Large Cell Carcinomas: Also known as undifferentiated carcinoma, this type of lung cancer is the least common type of Non-Small Cell Lung Cancers and comprises of about 10% to 15% of all lung cancers. Large Cell Lung Carcinomas frequently spreads to the lymph nodes and other distant sites of the body.

There are other types of lung cancers which are much less common than Small Cell Lung Cancers and Non-Small Cell Lung Cancers and together account for only 5% to 10% of lung cancers. These other types of lung cancers are:

Bronchial Carcinoids. This type of lung cancer accounts for about 5% of lung cancers and the tumors of this cancer are usually small, about 3 to 4 cm or less in size upon diagnosis. Bronchial Carcinoids are not related to smoking and commonly develop in people under the age of 40. Carcinoid tumors can spread and a small part of these tumors release hormone-like substances. The growth and spread of the Bronchial Carcinoids is slower and most of them are detected early and can be removed surgically.

Metastatic cancers originating from other primary tumors in the body which spread to the lungs are commonly found. Tumors present in any location of the body can metastasize to the lungs either through the lymphatic system, through the bloodstream or directly from the adjacent organs. Metastatic tumors of the lungs are commonly multiple and are scattered throughout the lungs. Metastatic tumors are more concentrated in the outer regions of the lungs than the central part of the lungs.

Cancers occurring in the supporting lung tissue such as blood vessels, smooth muscle or cells that are related to immune response occur rarely in the lungs.