Companion Diagnostic FDA Review Flexibilities: An Assessment of CDx for NSCLC to Support Aligned Approaches for Validation.

The U.S. Food and Drug Administration (FDA) recommends concurrent development of targeted therapies with an associated companion diagnostic (CDx) as the optimal approach to provide patient access to novel, safe, and effective treatments. However, CDx validation often relies on clinical samples from pivotal clinical trials for the drug, which can be challenging, particularly when there is limited sample availability. A review of Summary of Safety and Effectiveness Data (SSED) documents for CDx approved for non-small cell lung cancer (NSCLC) revealed that CDx for rare biomarkers often use alternative samples for validation. While the practice of using alternative samples for validation occurs, it is not always clear when these flexibilities are considered or how alternative samples should be used for validation. To address this, we propose the FDA establish guidance for the use of alternative sample sources for CDx validation, especially for rare biomarkers, to ensure timely and effective patient access to targeted therapies.