Lung cancer is the second most common cancer (excluding skin cancer) in men and women in the United States, but it is by far the leading cause of cancer deaths.
More than 500,000 Americans live with lung cancer and 234,030 new cases are diagnosed annually, causing 25 percent of cancer deaths. In fact, lung cancer accounts for more deaths than colon, prostate, and breast cancers combined. 
Lung cancer forms when abnormal cells in the lungs start to grow rapidly out of control. These cells-which typically start in the lining of the bronchi, bronchioles, or alveoli-can develop into a tumor and spread (or metastasize) to other parts of the body, such as your bones or brain.
Non-small cell lung cancer (NSCLC)
Non-small cell lung cancer accounts for about 85 percent of lung cancer cases. NSCLC is an umbrella term for several subtypes of lung cancer, but they are often referred to as one group because they have similar treatments.
Mainly occurring in smokers, adenocarcinomas start in young cells that produce substances like mucus, usually forming on the outer areas of the lung. They make up 40 percent of lung cancers, affect more women than men, and often grow slowly.
Squamous cell (epidermoid) carcinoma
This type of NSCLC begins in young squamous cells that make up the inner lining of your airways. Accounting for 25 to 30 percent of lung cancers, squamous cell carcinomas often pop up toward the center of the lungs near the bronchus (a major air passage).
Large cell (undifferentiated) carcinoma
Appearing throughout various parts of the lung, large cell carcinomas tend to grow and spread aggressively, so they are difficult to treat. They make up 10 to 15 percent of lung cancers. 
This rare form of NSCLC only makes up an estimated 0.4 to 4 percent of all lung carcinomas and includes components of both adenocarcinoma and squamous cell carcinoma. It mainly affects older men who have a history of smoking and tends to be difficult to treat. 
This extremely rare NSCLC only accounts for 0.1 to 0.4 percent of lung cancers. These large tumors affect the central airways of the lungs or the outer portion of the chest wall. Most commonly impacting older men and smokers, sarcomatoid carcinomas have a poor prognosis-a 5-year survival rate of only 20 percent. 
These tumors-which make up only 1 to 2 percent of lung cancers-are made up of neuroendocrine cells (cells in the lung that aids in air and blood flow control, growth of other lung cells, and oxygen detection), grow more slowly than other types of lung cancer, and don’t tend to spread. They can form near the center or outer portion of the lungs. 
Small cell lung cancer
Small cell lung cancer is also called oat cell cancer and makes up 10 to 15 percent of lung cancers. These larger tumors typically spread faster than NSCLC and are more common in heavy smokers. Small cell lung cancer commonly begins within the airways in the middle of the chest.