出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2014/09/30 07:41:21」(JST)
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Survival rate is a part of survival analysis, indicating the percentage of people in a study or treatment group who are alive for a given period of time after diagnosis. Survival rates are important for prognosis, but because this rate is based on the population as a whole, an individual prognosis may be different depending on newer treatments since the last statistical analysis as well as the overall general health of the patient.[citation needed] There are various types of survival rates (discussed below). They often serve as endpoints of clinical trials.
Patients with a certain disease (for example, colorectal cancer) can die directly from that disease or from an unrelated cause (for example, a car accident). When the precise cause of death is not specified, this is called the overall survival rate or observed survival rate. Doctors often use mean overall survival rates to estimate the patient's prognosis. This is often expressed over standard time periods, like one, five, and ten years. For example, prostate cancer has a much higher one year overall survival rate than pancreatic cancer, and thus has a better prognosis.
When someone is interested in how survival is affected by the disease, there is also the net survival rate, which filters out the effect of mortality from other causes than the disease. The two main ways to calculate net survival are relative survival and cause-specific survival or disease-specific survival.
Relative survival has the advantage that it does not depend on accuracy of the reported cause of death; cause specific survival has the advantage that it does not depend on the ability to find a similar population of people without the disease.
Relative survival is calculated by dividing the overall survival after diagnosis of a disease by the survival as observed in a similar population that was not diagnosed with that disease. A similar population is composed of individuals with at least age and gender similar to those diagnosed with the disease.
Cause-specific survival is calculated by treating deaths from other causes than the disease as withdrawals from the population that don't lower survival, comparable to patients who are not observed any longer, e.g. due to reaching the end of the study period.
Median survival is also commonly used in regards to survival rates, meaning the amount of time at which 50% of the patients have died and 50% have survived.[citation needed]
Five-year survival rate measures survival at 5 years after diagnosis.
In cancer research, various types of survival rate can be relevant, depending on the cancer type and stage. These include the disease-free survival (DFS) (the period after curative treatment [disease eliminated] when no disease can be detected), the progression-free survival (PFS) (the period after treatment when disease [which could not be eliminated] remains stable, that is, does not progress), and the metastasis-free survival (MFS) or distant metastasis–free survival (DMFS) (the period until metastasis is detected). Progression can be categorized as local progression, regional progression, locoregional progression, and metastatic progression.
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