In a twist, amanitin, the deadly toxin from death cap mushroom (Amanita phalloides), shuts down RNA Polymerase II, halting all protein production and killing both fast-growing and dormant cancer cells that often survive conventional treatments. In prostate-cancer models, the amanitin-based drug HDP-103 produced durable anti-tumor responses, remained active for 5–10 days, and outperformed comparable anti-PSMA cancer drugs while showing manageable liver and kidney side effects. A toxin responsible for fatal mushroom poisonings is now being engineered into precision therapies for multiple myeloma and advanced prostate cancer. Please do not ingest these mushrooms, this is clinical research in the early stages at best and using a very specific drug formula.