Types  There are several types of small cell lung cancer, defined by the tumor's appearance under the microscope. These include small cell, mixed small cell/large cell and combined small cell. It is unclear whether these types of tumor have different prognoses.
    This tumor arises from what are called neuroendocrine cells and is known as an APUD (amine precursor uptake decarboxylation) tumor. Under the electron microscope, hormone-producing (neurosecretory) granules can be seen. These tumors, therefore, can abnormally produce hormones and cause what have been known as paraneoplastic syndromes. For example, if the tumor produces too much cortisone , the condition is called Cushing's syndrome . If antidiuretic hormone (ADH) is produced, water is retained in the body and the apparent salt (sodium) level decreases. Each of these paraneoplastic syndromes produces its own signs and symptoms.

How It Spreads  Small cell lung cancer can spread via lymphatic vessels to the lymph nodes in the center of the lung (hilar nodes), the center of the chest (mediastinal nodes), in the neck and above the collarbone (supraclavicular nodes), and in the abdominal cavity. It is likely to spread through the bloodstream to the liver, lungs, brain and bone.

What Causes It  Cigarette smoking has been a major factor in the development of both small cell and non-small cell lung cancers. The increase in cigarette smoking by men in the 1920s, apparently related to increased cigarette advertising about that time, was followed in the 1940s by a dramatic increase in the incidence