Biomarker tests help employers control costs by eliminating trial-and error prescribing and subsequent exposure of patients to medications that may be ineffective and have harmful side effects. These tests are based on substances found in blood, bodily fluid or tissue and serve as a measurable way of predicting how a patient will to respond to treatment. Biomarker testing is an important tool of precision medicine that ensures patients get the treatment most likely to work for them, while minimizing costs due to ineffective treatments.