The relationship between small-cell and non-small cell lung cancers can be described by the following:

b. Of all lung cancers, approximately 80% are non-small cell and 20% are small cell

Although small cell and non-small cell lung cancers do differ by histology and clinical behavior, they probably have a common origin since c-myc or n-myc amplified small cell lung cancer lines will undergo transition to non-small cell phenotypes after insertion of an activated ras/gene. The overall incidence of lung cancers is 80% non-small cell and 20% small cell. Only the small cell carcinoma is predictably responsive to chemotherapy.

The staging system for small cell lung cancer is based on limited vs. extensive disease outside of a tolerable radiotherapy portal while the International Staging System uses TNM descriptors for 4 clinical stages. Unfortunately, only about 30% of patients with non-small cell lung cancer have potentially resectable tumors.