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Metastasis, or metastatic disease, is the spread of a cancer or other disease from one organ or part to another not directly connected with it. The new occurrences of disease thus generated are referred to as metastases (sometimes abbreviated "mets"). It was previously thought that only malignant tumor cells and infections have the capacity to metastasize (also spelled metastasise); new research has caused this to be reconsidered. The existence of metastatic cancers in the absence of primary tumors also suggests that metastasis is not always caused by malignant cells that leave primary tumors. Metastasis is a Greek word meaning "displacement", from μετά, ''meta'', "next", and στάσις, ''stasis'', "placement". Cancer occurs after a single cell in a tissue is progressively genetically damaged to produce cells with uncontrolled proliferation. This uncontrolled proliferation by mitosis produces a primary heterogeneic tumour. The cells which constitute the tumor eventually undergo metaplasia, followed by dysplasia then anaplasia, resulting in a malignant phenotype. This malignancy allows for invasion into the circulation, followed by invasion to a second site for tumorigenesis. Some cancer cells acquire the ability to penetrate the walls of lymphatic and/or blood vessels, after which they are able to circulate through the bloodstream (circulating tumor cells) to other sites and tissues in the body. This process is known (respectively) as ''lymphatic'' or ''hematogenous'' spread. After the tumor cells come to rest at another site, they re-penetrate the vessel or walls and continue to multiply, eventually forming another clinically detectable tumor. This new tumor is known as a metastatic (or ''secondary'') tumor. Metastasis is one of three hallmarks of malignancy (contrast benign tumors).〔 〕 Most neoplasms can metastasize, although in varying degrees (e.g., basal cell carcinoma rarely metastasize).〔 When tumor cells metastasize, the new tumor is called a ''secondary'' or ''metastatic'' tumor, and its cells are similar to those in the original tumor. This means, for example, that, if breast cancer metastasizes to the lungs, the secondary tumor is made up of abnormal breast cells, not of abnormal lung cells. The tumor in the lung is then called ''metastatic breast cancer'', not ''lung cancer''. == Signs and symptoms == Initially, nearby lymph nodes are struck early.〔 The lungs, liver, brain, and bones are the most common metastasis locations from solid tumors.〔 *In lymph nodes, a common symptom is lymphadenopathy *Lungs: cough, hemoptysis and dyspnea〔 (shortness of breath) *Liver: hepatomegaly (enlarged liver), nausea〔 and jaundice〔 *Bones: bone pain,〔(National Cancer Institute: Metastatic Cancer: Questions and Answers ). Retrieved on 2008-11-01〕 fracture of affected bones〔 *Brain: neurological symptoms such as headaches,〔 seizures,〔 and vertigo.〔 Although advanced cancer may cause pain, it is often not the first symptom. Some patients, however, do not show any symptoms.〔 When the organ gets a metastatic disease it begins to shrink until its lymph nodes burst, or undergo lysis. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Metastasis」の詳細全文を読む スポンサード リンク
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