Abstract
PURPOSE: Circulating tumor DNA (ctDNA) is an emerging tool in the evaluation of GI cancers. Challenges remain in defining its utility and role as a primary end point in therapeutic trials. The National Cancer Institute (NCI) ctDNA GI working group was created to evaluate current data and provide guidance on the inclusion of ctDNA in GI cancer trials. METHODS: The NCI GI steering committee assigned four task force members to serve as co-chairs for the working group. Co-chairs identified experts within each GI disease group to form a panel that convened to review data and provide recommendations. The group focused on ctDNA's role as a potential surrogate for assessing prognosis and guiding treatment decisions that may enhance GI cancer trials. A manuscript was drafted, circulated, revised, and voted on by the panel. The final draft was reviewed by the Cancer Therapy Evaluation Program. RESULTS: Further data are required to support ctDNA as a primary end point for late-phase therapeutic trials, particularly in studies that could change the standard-of-care. However, the group supports ctDNA as a primary efficacy end point for phase II studies and as a noninvasive evaluation strategy for new drug development. Incorporation of ctDNA as a biomarker in trial design must consider the specific context of disease biology of the GI cancer subtypes. ctDNA should be incorporated as an exploratory end point across a variety of disease settings and indications. Several practical considerations were identified to optimize the incorporation of ctDNA in future trial design. CONCLUSION: Prospective trials are required to clarify the role of ctDNA as a valid surrogate end point for progression-free or overall survival in GI cancers.