The weight of the enemy: Tumor burden as a tumor‐agnostic prognostic marker and the limits of immunotherapy

Baseline tumor burden is a powerful, tumor‐agnostic, prognostic marker across rare cancers, and patients with greater disease volume at treatment initiation face significantly worse survival, independent of cancer type. Critically, tumor burden predicts prognosis rather than immunotherapy response, underscoring that earlier diagnosis and earlier line intervention remain the most consequential opportunities to improve outcomes in rare malignancies.