SERPINA9 also known as centerin or GCET1 is a human gene. The protein encoded by this gene is a member of the serpin family of serine protease inhibitors.Highly expressed in normal germinal center (GC) B-cells and GC B-cell-derived malignancies.

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. Protease inhibitor that inhibits trypsin and trypsin-like serine proteases (in vitro). Inhibits plasmin and thrombin with lower efficiency (in vitro).