IL1B and neoplasm: Although neutralizing extracellular IL1α and IL1β individually had little impact on tumour sphere formation in vitro, simultaneous sequestering of IL1α and IL1β resulted in a drastic reduction of tumour sphere numbers (Fig. 7a and Supplementary Fig. 11a), suggesting that IL1α and IL1β are required, but likely to compensate each other, for maintaining tumour sphere-formation ability.