Chemotherapy is often seen solely as a tumor-targeting treatment, yet new evidence reveals a paradox: the tissue injury it causes can reprogram the body’s defenses, influencing the risk of metastasis. Researchers from the University of Lausanne and collaborators reported that chemotherapy reshapes the gut-immune axis by inducing microbiota-derived indole-3-propionic acid (IPA), which reprograms myelopoiesis to curb monocyte-driven immunosuppression and metastasis in colorectal cancer (CRC).