Episode
Cancer Blood Tests Part 2: The clinical trial
- Published
- Jun 29, 2026
- Duration seconds
- 3473
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Summary
How do you decide whether a clinical trial “worked”? In Part 2 of our Galleri series, we examine the landmark randomized trial of a blood test designed to detect more than 50 cancers. We explore why different outcome measures led to dramatically different headlines, discuss primary versus secondary outcomes, pre-registration, hierarchical testing, and post hoc analyses, and explain why mortality remains the outcome everyone is waiting for. Along the way, we uncover a statistical mystery involving dozens of missing cancers and discover how a little arithmetic can sometimes reveal more than a press release. Statistical topics cancer screening exploratory analyses hierarchical testing missing data multiple testing outcome measures post hoc analyses pre-registration primary and secondary outcomes randomized clinical trials screening tests Methodologic Morals “When the simple numbers don't add up, pay attention. The arithmetic may be trying to tell you something.” “The first question should not be, did it work? It should be, what counts as success?” References Giridhar KV, et al. Safety and performance results from PATHFINDER 2, a registrational study of a multi-cancer early detection test in an intended-use population . Presented at the 2026 American Society of Clinical Oncology (ASCO) Annual Meeting. May 2026. Hubbell E, Clarke CA, Aravanis AM, Berg CD. Modeled Reductions in Late-stage Cancer with a Multi-Cancer Early Detection Test. Cancer Epidemiol Biomarkers Prev . 2021;30(3):460-468. doi:10.1158/1055-9965.EPI-20-1134 Neal RD, Johnson P, Clarke CA, et al. Cell-Free DNA-Based Multi-Cancer Early Detection Test in an Asymptomatic Screening Population (NHS-Galleri): Design of a Pragmatic, Prospective Randomised Controlled Trial. Cancers (Basel) . 2022;14(19):4818. Publishe…