What is Lung Cancer?

Although lung cancer is the second most common form of cancer diagnosed, it is the number one cause of cancer related deaths in the United States. Fortunately, the number of new lung cancer cases and deaths reported in recent years is declining due to a decline in smoking, better diagnostic tools, and new treatment options. Approximately 350,000 people are living with lung cancer at any given time.

Cancer is a condition in which cells multiply uncontrollably to form growths (called tumors) that invade and destroy normal tissue. (Tumors also can be benign—non-cancerous.) Cancer cells can spread from their original site to other parts of the body in a process known as metastasis.

Cancers are named for the place in the body where they begin, not where they may spread. Lung cancer begins in the lungs—two bullet-shaped organs that are part of the respiratory system. Each lung is contained in a sac called the pleura. The right lung has three sections (lobes), and the left lung has two lobes. Lung cancer is sometimes called bronchogenic cancer because most cases begin in the cells of one of the lungs' breathing tubes, called bronchi.

There are two main categories of lung cancer—non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC)—and several subtypes of NSCLC. In the United States, 80% to 85% of people diagnosed with lung cancer have NSCLC.
The difference between NSCLC and SCLC has to do with the cell of origin that becomes cancerous. It also involves the appearance of the cells, how quickly each type spreads to other parts of the body, and how each tumor type responds to treatment.

Non-Small Cell Lung Cancer (NSCLC)

NSCLC comprises 80-85% of all lung cancers and has three major subtypes: 

  • Adenocarcinoma 
  • Squamous cell carcinoma (formerly called epidermoid carcinoma) 
  • Large cell carcinoma 


  • Accounts for 35-50% of the NSCLC lung cancer cases in the United States 
  • Is the most common lung cancer diagnosed in women 
  • Usually starts near the outer edges of the lungs 
  • May occur in those with a history of smoking but is the type most often found in those who never smoked 

Squamous cell carcinoma

  • Represents about 30% of NSCLC lung cancers in the United States 
  • Usually starts in one of the bronchi 
  • Frequently spreads to regional lymph nodes 
  • Is strongly associated with smoking 

Large cell carcinoma

  • Represents about 10% of NSCLC lung cancers in the United States 
  • May start in any part of the lung 
  • Is frequently the diagnosis when other types of lung cancer have been ruled out


Small Cell Lung Cancer

Small Cell Lung Cancer represents 15% to 20% of all lung cancers in the United States. This form typically grows more rapidly than NSCLC and spreads to the lymph nodes and other organs more quickly. It is seen predominantly in smokers or former smokers (about 98% of cases are attributed to smoking.) SCLC usually starts in one of the larger bronchi. At the time of diagnosis, it usually has spread and is considered a systemic disease. SCLC is more responsive to a variety of chemotherapy drugs. This form was previously called "oat cell" cancer because the cells are small and oval, like oat grains.

The more you know about your particular type of lung cancer, the better you will be able to make treatment decisions.

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