Serpin A9 also known as centerin or GCET1 is a protein that in humans is encoded by the SERPINA9 gene located on chromosome 14q32.1.[1] Serpin A9 is a member of the serpin family of serine protease inhibitors. The expression of SERPINA9 is restricted to germinal center B cells and lymphoid malignancies. SERPINA9 is likely to function in vivo in the germinal center as an efficient inhibitor of trypsin-like proteases. Highly expressed in normal germinal center (GC) B-cells and GC B-cell-derived malignancies.