Proton Cancer Centre Health care professionals broadly classify lung cancers into two types: small-cell lung cancers (SCLC) and non-small-cell lung cancers (NSCLC). This classification depends upon the microscopic appearance of the tumor cells themselves, specifically the size of the cells. These two types of cancers grow and spread in different ways and may have different treatment options. SCLC comprises about 20% of lung cancers which are the most aggressive and rapidly growing of all lung cancers. SCLC is related to cigarette smoking, with only 1% of these tumors occurring in non-smokers. SCLC metastasis rapidly spreads to many sites within the body and are most often discovered after they have spread extensively. Referring to a specific cell appearance often seen when examining samples of SCLC under the microscope, these cancers are sometimes called oat cell carcinomas. NSCLC is the most common lung cancers, accounting for about 80% of all lung cancers. NSCLC can b