Primary lung cancers arise from cells in the lung. There are several types of primary lung cancer. The two most common types are called small-cell lung carcinoma (SCLC) and non-small-cell lung carcinoma (NSCLC). NSCLCs include squamous cell cancers (the most common type of lung cancer), adenocarcinoma and large-cell carcinoma. About 1 in 5 cases of lung cancer are SCLC; the remainder is NSCLC. All these types of lung cancer arise from various cells which line the airways (bronchi).
Each type of lung cancer has different properties. For example, small-cell carcinoma grows and spreads (metastasizes) rapidly. By the time a small-cell cancer is diagnosed, in most cases, it has already spread to other parts of the body. In contrast, a squamous cell carcinoma tends to grow more slowly and may not spread to other parts of the body for some time.