Multigene panel testing for hereditary tumor syndromes: an engine for stratified, preemptive cancer medicine in Japan

Multigene panel testing (MGPT) is usually discussed as a diagnostic technology. Its more important role, however, is to enable a proactive stance toward inherited cancer risk-using an individual's germline information to go on the offensive against cancer rather than waiting for it to declare itself. Reframed this way, MGPT is the engine of stratified, preemptive cancer medicine: care that acts on genetic risk to intercept cancer before it arises. Framed by the definition of cancer genomic medicine-care that optimizes treatment, predicts prognosis, and prevents disease onset using genomic information from the tumor and germline of patients with cancer, sometimes extending to unaffected individuals and to multi-omics information beyond the genome-preemptive medicine is placed at the center; the Japanese Society for Hereditary Tumors, in its 2025 Guidance-which spans diagnosis, prevention, and treatment across 56 genes-provides the map for this approach in Japan. At its heart is the preventive arm: cascade testing and the fiscal-year 2026 reimbursement revision carry protection to unaffected pathogenic variant carriers before cancer begins, in a "leave-no-one-behind" model of cancer control. This review then examines how this continuum is delivered (team-based care, with attention to disparities), enabled (quality assurance, Japan's framework for laboratory-developed tests (LDTs), and social implementation through insurance), and-central to this feature-how it must integrate host biology. Because treatment optimization depends on whether the host can benefit, sarcopenia assessment is a natural preemptive companion to germline testing-the host-biology foundation on which treatment is optimized, so that germline genetics and host biology are integrated rather than read in isolation.