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Cancer slope factor
Cancer slope factors (SF) are used to estimate the risk of cancer associated with exposure to a carcinogenic or potentially carcinogenic substance. A slope factor is an upper bound, approximating a 95% confidence limit, on the increased cancer risk from a lifetime exposure to an agent by ingestion or inhalation. This estimate, usually expressed in units of proportion (of a population) affected per mg of substance/kg body weight-day, is generally reserved for use in the low-dose region of the dose-response relationship, that is, for exposures corresponding to risks less than 1 in 100.〔http://www.epa.gov/iris/help_ques.htm〕
Slope factors are also referred to as cancer potency factors (PF).
==Toxicity Assessments for Carcinogenic Effects==
For carcinogens, it is commonly assumed that a small number of molecular events may evoke changes in a single cell that can lead to uncontrolled cellular proliferation and eventually to a clinical diagnosis of cancer. This toxicity of carcinogens is referred to as being "non-threshold" because there is believed to be essentially no level of exposure that does not pose some probability of producing a carcinogenic response, therefore, there is no dose that can be considered to be risk-free. However, some (non-genotoxic) carcinogens may exhibit a threshold whereby doses lower than the threshold do not invoke a carcinogenic response.
When evaluating cancer risks of genotoxic carcinogens, theoretically an effect threshold cannot be estimated. For chemicals that are carcinogens, a two-part evaluation to quantify risk is often employed in which the substance first is assigned a weight-of-evidence classification, and then a ''slope factor'' is calculated.〔http://www.epa.gov/oswer/riskassessment/ragsa/pdf/ch7.pdf〕
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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