Small cell carcinomas (SCC) commonly arise in the respiratory tract; however, it is not uncommon for these cells to arise in nonpulmonary sites, as extrapulmonary small cell carcinoma (EPSCC).  Small cell carcinoma is a distinct clinical and pathologic entity that arises from cells of the amine precursor uptake and decarboxylation (APUD) system.
Extrapulmonary small cell carcinoma is estimated to account for approximately 1000 new cancer cases per year in the United States. This number, however, appears to be an underestimation. Most available literature on this condition exists in the form of case reports and retrospective series. The role of local and systemic therapies for extrapulmonary small cell carcinoma treatment is still not clearly defined. Most reports indicate chemotherapy sensitivity and response rates similar to those seen in small cell lung cancer with similar chemotherapeutic regimens. Surgery appears to play a more important role in the management of extrapulmonary small cell carcinoma compared to the role of surgery for small cell lung cancer.
Histologic criteria for diagnosis of extrapulmonary small cell carcinoma are same as those for pulmonary small cell carcinoma, that is appearance of uniform small cells with sparse cytoplasm, dense nuclei, and inconspicuous nucleoli.  Since extrapulmonary small cell carcinoma has been reported from multiple sites, it is thought that the cell of origin is identical and derives from those originating in neural crest and then migrating to different epithelial sites within the body. These cells are characterized by presence of intracytoplasmic neurosecretory granules and stain positively with chromogranin.
Extrapulmonary small cell carcinoma has been reported to arise in almost all body sites except the central nervous system. [3, 4] Primary sites may include esophagus, salivary glands, gastrointestinal tract (including small intestine and large intestine), pancreas, larynx, cervix uteri, uterus, urinary bladder, prostate, breast, and lacrimal gland in addition to skin, where it is also referred to as Merkel cell carcinoma. 
Like pulmonary small cell carcinoma (lung cancer), small cell carcinomas arising from extrapulmonary sites may be associated with paraneoplastic syndromes, notably syndrome of inappropriate secretion of antidiuretic hormone (SIADH) and hypercalcemia. However, deletions of chromosome arm 3p and c-myc amplification described in small cell pulmonary carcinoma have not been reported in extrapulmonary sites.
Approximately 1000 cases of extrapulmonary small cell carcinoma are reported annually, with an overall incidence of 0.1-0.4% of all cancers.
Global incidence of extrapulmonary small cell carcinoma is unknown.
Because most of the literature is retrospective and in the form of case reports, estimating mortality rates is difficult. In addition, not all reported cases are managed uniformly, thereby making it further difficult to estimate prognosis. Long-term survival is, however, reported, especially in those treated with an aggressive multimodality approach.
Extrapulmonary small cell carcinoma may have a similar prognosis to that of small cell lung cancer. Those presenting with disseminated disease have a very poor prognosis and short survival time despite management with chemotherapy, radiation therapy, or both. Long-term survival is reported in those presenting with localized disease. 
No predilection for race or sex is clear in the reported literature. However, most of these malignancies develop after the sixth decade of life.
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