Although all cancers of solid organs have subtypes, they all are identified with a single identifying name based on the organ in which they originate. Colon cancer and pancreatic cancer, for example. Lung cancer is different: from the outset, based on the appearance of cells under the microscope, it is referred to as either small cell lung cancer (SCLC) or non-small cell lung cancer (NSCLC). In earlier times SCLC was termed oat cell as an imaginative physician fancied a resemblance between its microscopic appearance and oats. This terminology is no more.

Roughly two thirds of new cancers are of the NSCLC type and one third are SCLC. This distinction is clinically useful. These lung cancers not only differ in their appearance under the microscope but, more importantly, exhibit dissimilar biologic behaviors which takes their treatment algorithm in different directions.

SCLCs disseminate and spread so much earlier than NSCLC with metastases to either distant organs or lymph nodes or both that the patient requires systemic treatment with chemotherapy or immunotherapy. Radiation may be added but the systemic treatments are always necessary. Also, since surgery is only helpful for any patient if there is the ability to remove all malignant cells, operative intervention is rarely appropriate.

NSCLC, which itself can be subclassified by cell type, including adenocarcinoma, squamous cell cancer and, confusingly, large cell cancer, spreads more slowly; therefore, a treating physician is more likely to find in a new patient that the cancer is confined to the lung. If information derived from staging studies shows this to be the case an operation to remove the tumor and surrounding lung has the potential to be curative. Adjuvant treatment (administered after surgery) with systemic agents or even neoadjuvant treatment (given before surgery) is added for some patients.