- A serine proteinase inhibitor locus at 18q21.3 contains a tandem duplication of the human squamous cell carcinoma antigen gene. Schneider, S.S., Schick, C., Fish, K.E., Miller, E., Pena, J.C., Treter, S.D., Hui, S.M., Silverman, G.A. Proc. Natl. Acad. Sci. U.S.A. (1995)