Overall, we demonstrate that FLASH irradiation reduces IFN‐β secretion in non‐tumorigenic MCF‐10A cells by enhancing the cytochrome c leakage and caspase activation, while it can increase IFN‐β secretion in MDA‐MB‐231 carcinoma cells by suppressing the apoptotic caspases. Here, CYCS is linked to carcinoma.