Diagnostic assays are tests performed on bodily samples (blood, tissue, urine, etc.) to identify and measure biomarkers. Hospitals and labs use these assays to diagnose conditions, determine treatment options, or monitor risk factors by detecting the presence, quantity, and activity of specific biomarkers in the samples.

For example, a blood test that detects circulating tumor DNA (ctDNA) levels or digital pathology tools that assess biomarkers in a tissue biopsy are considered diagnostic assays. Read more on Friends’ ctDNA Portfolio and Digital Pathology Project.

Companion Diagnostics (CDx) are tests that can identify patients who are most likely to benefit from a particular therapeutic product, identify patients likely to be at increased risk for serious side effects as a result of treatment with a particular therapeutic product, or monitor response to treatment with a particular therapeutic product for the purpose of adjusting treatment to achieve improved safety or effectiveness.

For example: trastuzumab is a targeted therapy used to treat certain breast cancers. It works by acting on the receptor for a protein called “HER2/neu.” Trastuzumab is primarily beneficial in cases where patients overexpress HER2. Physicians build confidence in prescribing an effective drug by using a companion diagnostic to test patients for overexpression of HER2 before recommending trastuzumab.