Multicancer Detection Assays: Promise and Potential Harms of a Novel Cancer Screening Tool.

Multicancer detection (MCD) tests are an emerging innovation in cancer screening that use blood samples to detect multiple cancer types at once, potentially identifying malignancies earlier and with greater accessibility than traditional, site-specific screening methods. Several tests have demonstrated the ability to detect cancer signals and suggest tissue of origin, which may enhance screening for cancers with existing screening tests and fill critical gaps for cancers lacking effective screening modalities. However, MCD testing raises concerns about the potential for substantial harm, including false-positive test results leading to short-term emotional distress and wasteful and potentially risky testing, unwarranted reassurance when results are falsely negative, the identification of indolent cancers (overdiagnosis), and increased strain on health care resources. Unclear follow-up protocols and limited harms reporting further complicate their use. Equity issues persist, as clinical trials may lack diverse representation and potentially miss population-specific risks. To ensure that MCD tests provide a net benefit to patients and to minimize the burden on health systems, rigorous evaluation, transparent harms reporting, and the implementation of robust practices for follow-up and shared decision-making are essential. As these tests evolve and their use becomes more widespread, careful integration into existing screening practices will be key to maximizing benefit while minimizing unintended consequences.