A primary lung cancer tumor — one which has begun in the lungs, and has not spread from somewhere else in the body — can be diagnosed as small cell lung cancer (SCLC). These tend to make up 10 to 15 percent of lung cancers, with the rest being of the non-small cell lung cancer (NSCLC) type. A correct diagnosis of  lung cancer type is essential to determining an effective treatment plan, as different types of cancer react to treatment differently and can spread at different rates.

SCLC is so named because of the appearance of cancer cells under the microscope, as they are much smaller than in NSCLC. Small cell lung cancer is also called “oat cell cancer” based on the shape of cells. It is a type of lung neuroendocrine tumor, affecting the neuroendocrine system used to send messages between cells and different part of the body. SCLC is the most aggressive type of lung cancer, and generally occurs only in heavy smokers.


SCLC tumors tend to develop and spread very quickly compared to NSCLC. Once the cancer has begun spreading, it is said to be “metastatic.” At this point, the cells are able to break away from the primary tumor and form a new tumor elsewhere by traveling through the blood or lymph system, a vital part of the immune system. Two defined stages of SCLC exist: limited or extensive stage.

The cancer is defined as limited stage if the tumor is only present in the lung where it started, or has only spread to the immediate area around the tumor, such as the space between the lungs, or the nearest lymph node above the collarbone. If the cancer is extensive stage, it has spread beyond the originally affected lung. This includes the opposite lung, the lymph nodes that are further away, or other parts of the body including bone marrow.

As SCLC tumors spread quickly, only one-third of patients tend to be in limited stage when the cancer is first diagnosed.

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