Interpreting Breast Cancer Statistics: The Difference Between Absolute and Relative Breast Cancer Risk Factors

A risk factor can be defined as something that may increase your chance of getting breast cancer. There are two ways that scientists define risk factors: absolute and relative. An absolute breast cancer risk factor is the chance a particular group of people will develop breast cancer over a specific time period of time. For example, if you are a woman, you have a 1 in 8 (or 12.5%) chance of developing breast cancer in your lifetime. A relative breast cancer risk factor compares how something specific, (like inheriting a BRCA1 or BRCA2 gene mutation), will change your risk compared to those who don’t have that specific thing. So, if a woman who has a BRCA1 or BRCA2 gene mutation has up to an 80% chance in relative risk of receiving a breast cancer diagnosis during her lifetime (and at a younger age) over those who don’t, what does that breast cancer statistic mean? Multiply the absolute risk of 12.5% by the relative risk of 80%. The answer is 10%. So 10% is the size of the increase in risk. Then add the 10% increase in risk to the 12.5% risk, and she has a 22.5% absolute risk of breast cancer during her lifetime, at a younger age, if she has inherited a BRCA1 or BRCA2 gene mutation. It is important to know the difference between absolute and relative risk so you can determine how certain breast cancer statistics apply to you.