We propose the novel concept that IL-17B plays a critical role in the homeostasis of CSCs based on the following evidence obtained in the present study: (1) IL-17RB was highly expressed in LGR5+ CSCs, (2) IL-17B promoted the sphere-formation ability of CSCs in vitro and enhanced tumor growth, invasion and stemness in vivo, and (3) knockdown of IL-17RB in CSCs reversed the sphere-formation ability induced by IL-17B. The gene discussed is IL17B; the disease is neoplasm.