Beyond the Scan: Biomarker Access, Diagnostic Equity, and the Case for a Shared Regulatory Path in Alzheimer's Disease and Cancer

Two earlier papers in this research program each touched on biomarker access briefly, once while explaining why disease-modifying Alzheimer's trials carry unusually steep eligibility barriers, once while explaining why gastric cancer trials do the same. Neither paper had room to ask the larger question sitting underneath both findings: whether the diagnostic technology deciding who gets tested, and therefore who gets treated, is itself built and regulated in a way that reaches the people who need it. This paper takes up that question directly, across both diseases at once, and finds a pattern that neither disease-specific paper could have surfaced on its own. Alzheimer's disease and oncology are, right now, walking the same path a few years apart. Both fields built their diagnostic gold standards around procedures that are invasive, expensive, and geographically concentrated: amyloid-PET and cerebrospinal fluid sampling for Alzheimer's disease, and tissue biopsy for cancer, and both are now in the middle of a transition toward a blood-based alternative that could plausibly reach almost anywhere a blood draw is possible. For Alzheimer's disease, that transition already has an international regulatory home: a 2024 consensus effort has begun setting minimum performance standards for blood-based amyloid tests specifically because specialist access is limited or absent across much of the world. Oncology's equivalent, circulating tumor DNA testing, already has approved assays and a growing evidence base, but no comparable coordinated push to make sure it reaches low- and middle-income settings as it matures, despite a systematic review already proposing exactly the kind of implementation framework Alzheimer's disease diagnostics has begun to build. This paper lays out the shared shape of that problem across both diseases, the human and technological solutions already documented or actively proposed for each, and argues directly that oncology does not need to reinvent this regulatory path from nothing. It could, with deliberate effort, borrow one that Alzheimer's disease research has already started building.