In this new age of targeted therapy, thousands of putative biomarkers have been identified and published. We see the posters at every scientific meeting. These have dramatically increased the opportunities for developing more effective therapeutics. However, the transfer of biomarkers from discovery to clinical practice is still a process filled with lots of pitfalls and limitations. To become a clinically approved test, a potential biomarker should be confirmed and validated using hundreds of specimens and should be reproducible, specific and sensitive.
These two terms are often confusing and sometimes used interchangeably. There are no 100% sensitive and specific biomarkers for any tumor type to date. A biomarker with a high sensitivity has a low specificity and vice versa. Unfortunately, biomarkers with ideal specificity and sensitivity are difficult to find.
Sensitivity is the ability of a test to accurately identify a patient/tumor sample that has the characteristic for which it is being tested, For example, breast cancer patients who test positive for HER2 actually have an abundance of HER2 receptors on their tumor cells. Tests that report HER2 positivity when, in fact the patient does not have an abundance of HER2 receptors are called false positive.
Specificity, on the other hand is the ability of a test to accurately identify those who do not have the characteristic being tested for. In the HER2 example, patients testing negative for HER2 do not have overexpression of the HER2 receptor on their tumor cells. Therefore, tests reporting HER2 negative when, if fact there is HER2 overexpression, are called false negative.
Sensitivity and specificity are characteristics of the testing method, and are expressed in percentage. They confer confidence in the accuracy of the test results.