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Small Cell Lung Cancer
Small cell lung cancer is one of the two main types of lung cancer—non-small cell lung cancer being the other—and is named for the small size of the cancer cells when viewed under a microscope. Because these two types of lung cancer differ both in their outlook (prognosis) and course of treatment, they are generally considered separately. About 10% to 15% of all lung cancers are small cell lung cancers, which often develop near the center of the chest, grow and spread quickly, and have almost always spread to other parts of the body before they are detected. The other 85% to 90% of lung cancers are non-small cell lung cancers, which can be further characterized into three different subtypes: adenocarcinomas, squamous cell carcinomas, and large cell carcinomas. These pages will focus mainly on small cell lung cancer, except where data only exist for lung cancer as a whole.
Lung cancer (both small cell and non-small cell lung cancer) is the second most common cancer in the United States, representing about 13% of all new cancer cases. It is estimated that rub 221,000 and 410,000 people in the United States and Europe, respectively, will be diagnosed with lung cancer this year, and about 6.6% of men and women will be diagnosed with lung cancer at some point during their lifetime.
Tobacco smoke is the leading cause for the development of small cell lung cancer, and most deaths due to small cell lung cancer are associated with smoking or with exposure to secondhand smoke. Additional risk factors include exposure to radon, air pollution, or other chemicals. Although these environmental factors are the predominant risk factors for small cell lung cancer, genetic factors may also play role in the development of some cancers.
It is estimated that each year, about 158,000 and 354,000 people die of lung cancer in the United States and Europe, respectively. About 17% of patients survive 5 years or more after being diagnosed with lung cancer. For patients with localized lung cancers that have not spread, the 5-year survival rate is 55%. For patients with tumors that have spread to regional lymph nodes within the chest, the 5-year survival rate is 27%. For patients with tumors that have spread to more distant parts of the body, the 5-year survival rate is about 4%.
There are two types of small cell lung cancer: small cell carcinoma and combined small cell carcinoma. Combined small cell carcinoma is a relatively uncommon tumor in which some cells have characteristics of small cell carcinoma and other cells with characteristics of non-small cell lung cancers. The clinical characteristics of these two cancer types are not significantly different, and the overall survival and course of treatment is similar.
When comparing tumors, small cell lung cancers can vary greatly in the exact molecular changes that have occurred to transform healthy cells into cancerous cells. Nevertheless, nearly all small cell lung cancers have lost two key genes responsible for preventing uncontrolled cell growth (TP53 and RB1). Other common genetic changes include the deletion of large amounts of DNA from chromosome 3, as well as the abnormal activation of cellular growth and survival processes.
Most lung cancers do not cause any symptoms until they’ve reached an advanced stage and are difficult to cure, but some people with early lung cancer do have symptoms. Common symptoms include: a persistent cough, chest pain, hoarseness, weight loss and loss of appetite, coughing up blood, shortness of breath, feeling tired or weak, lung infections like bronchitis or pneumonia, or new onset of wheezing. Additionally, lung cancer that has spread can cause bone pain, neurologic changes, yellowing of the skin and eyes, or lumps under the surface of the skin.
Lung cancer staging uses a three-part system, in which the Tumor size, the spread to lymph Nodes, and the spread to other organs (Metastasis) is evaluated. This TNM system is then used to assign an overall stage of 0, I, II, III, or IV to the cancer. It should be noted that some of these stages can be further divided into sub-stages, depending on the tumor’s size, lymph node involvement, and spread to distant sites.
In stage 0, cancer cells are only found in the topmost layers of the air passages, and have not invaded deeper into the lung tissue nor spread to lymph nodes or other sites. Stage I tumors are no larger than 5 cm, and have not spread to lymph nodes or to distant organs, whereas stage II tumors can be larger and may or may not have spread to lymph nodes on the same side as the primary tumor. Stage III tumors can be any size, and generally have spread to lymph nodes on the same side as the primary tumor, as well as potentially having spread to lymph nodes on the opposite side. In stage IV, the tumor has spread to the other lung or to other organs such as the liver, bones, or brain.
Most patients with small cell lung cancer receive a combination of two chemotherapy drugs as a first-line therapy. Additional radiation therapy may be used simultaneously with the chemotherapy, or after chemotherapy has ended. Surgery is rarely used as the main treatment in small cell lung cancer.