What Is Lung Cancer?

Although lung cancer is the leading cause of cancer death in the U.S. in both men and women, it is also one of the most preventable kinds of cancer. At least four out of five cases are associated with cigarette smoking, and the cause-and-effect relationship has been extensively documented. During the 1920s, large numbers of men began to smoke cigarettes, presumably in response to increased advertising. Twenty years later, the frequency of lung cancer in men climbed sharply. In the 1940s, significantly more women became smokers. Twenty years later, there was a similar dramatic increase in lung cancer among women.

Lung tumors almost always start in the spongy, pinkish gray walls of the bronchi -- the tubular, branching airways of the lungs. More than 20 types of cancerous tumors that originate in the lung itself -- primary lung cancer -- have been identified. The major types of lung cancer are small-cell lung cancer and non-small cell lung cancer. The more common non-small cell variety is further divided into squamous cell carcinoma, adenocarcinoma, large-cell carcinoma, and more. Mixed tumors may also occur.

What are the types of lung cancer?

Lung cancers, also known as bronchogenic carcinomas ("carcinoma" is another term for cancer), are broadly classified into two types: small cell lung cancers (SCLC) and non-small cell lung cancers (NSCLC). This classification is based upon the microscopic appearance of the tumor cells. These two types of cancers grow, spread, and are treated in different ways, so a distinction between these two types is important.

Small Cell Lung Cancer comprises about 10%-15% of lung cancers. This type of lung cancer is the most aggressive and rapidly growing of all the types. SCLC is strongly related to cigarette smoking with only 1% of these tumors occurring in non-smokers. SCLCs metastasize rapidly to many sites within the body and are most often discovered after they have spread extensively. 

General Information about Small Cell Lung Cancer

Small cell lung cancer (SCLC) accounts for approximately 15% of bronchogenic carcinomas. At the time of diagnosis, approximately 30% of patients with SCLC will have tumors confined to the hemithorax of origin, the mediastinum, or the supraclavicular lymph nodes. These patients are designated as having limited-stage disease (LD). Patients with tumors that have spread beyond the supraclavicular areas are said to have extensive-stage disease (ED). SCLC is more responsive to chemotherapy and radiation...

Non-Small Cell Lung Cancer is the most common lung cancer, accounting for about 85%-90% of all cases. NSCLC has three main types designated by the type of cells found in the tumor. They are:

  • Adenocarcinomas are the most common type of NSCLC in the U.S. and comprise up to 40% of NSCLC cases. While adenocarcinomas are associated with smoking like other lung cancers, this type is also seen in non-smokers -- especially women -- who develop lung cancer. Most adenocarcinomas arise in the outer, or peripheral, areas of the lungs. They also have a tendency to spread to the lymph nodes and beyond. Bronchioloalveolar carcinoma is a subtype of adenocarcinoma that frequently develops at multiple sites in the lungs and spreads along the preexisting alveolar walls. It may also look like pneumonia on a chest X-ray. It is increasing in frequency and is very common in non-smoking women and in the Asian population.
  • Squamous cell carcinomas were formerly more common than adenocarcinomas; at present they account for about 25% of NSCLC cases. Also known as epidermoid carcinomas, squamous cell cancers arise most frequently in the central chest area in the bronchi. This type of lung cancer most often stays within the lung, spreads to lymph nodes, and grows quite large, forming a cavity.
  • Large cell carcinomas, sometimes referred to as undifferentiated carcinomas, are the least common type of NSCLC, accounting for 10%-15% of all lung cancers. This type of cancer has a high tendency to spread to the lymph nodes and distant sites.

Other types of cancers can arise in the lung; these types are much less common than NSCLC and SCLC and together comprise only 5%-10% of lung cancers:

  • Bronchial carcinoids account for up to 5% of lung cancers. These tumors are generally small (3-4 cm or less) when diagnosed and occur most commonly in persons under age 40. Unrelated to cigarette smoking, carcinoid tumors can metastasize, and a small proportion of these tumors secrete hormone-like substances. Carcinoids generally grow and spread more slowly than bronchogenic cancers, and many are detected early enough to be surgically removed.
  • Cancers of supporting lung tissue such as smooth muscle, blood vessels, or cells involved in the immune response can rarely occur in the lung.

As mentioned previously, metastatic cancers from other primary tumors in the body are often found in the lung. Tumors from anywhere in the body may spread to the lungs either through the bloodstream, through the lymphatic system, or directly from nearby organs. Metastatic tumors are most often multiple, scattered throughout the lung and concentrated in the outer areas rather than central areas of the organ.