Studies using colon and melanoma tumour models demonstrated the role of 5‐FU in lowering tumour burden by activating the cancer cell's intrinsic cyclic GMP‐AMP synthase and the cyclic GMP‐AMP receptor stimulator of interferon genes (cGAS‐STING) pathway, which in turn triggers anti‐tumour activity. The gene discussed is CGAS; the disease is neoplasm.