BNF1 (breast tumor novel factor 1) was first identified as an mRNA differentially expressed between vascularized tumor breast tissue and adjacent normal tissue. BNF1 overexpression has been found in breast, lung, and colon tumors. BNF1 has also been identified as a differentially expressed mRNA during myoblast and osteoblast differentiation. BNF1 contains chordin-like cysteine-rich repeats and is part of a family of secreted proteins that associate with members of the TGF-beta superfamily. BNF1 displays an extensive and complex pattern of alternative splicing that results in several isoforms expressed in distinct tissue.