SFRP1 and neoplasm: Secreted frizzled-related protein 1 (SFRP1), a member of the SFRP family that contains a cysteine-rich domain, acts as a soluble modulator of Wnt signaling by directly interacting with Wnt (Nakajima et al., 2009), and plays a role in regulating the growth and differentiation of specific tumor cells.