Squamous cell carcinoma antigen (SCCA), a member of the serine protease inhibitor (serpin) family, is a subfraction of the tumor associated antigen TA-4, is a glycoprotein, with a molecular weight between 42 to 48 kDa. SCCA2 is a serological marker for squamous cell carcinomas (SCC). Elevated serum levels are correlated with the clinical stage of the disease.Schneider et al. (1995) demonstrated that 18q21.3 contains a cluster of serine proteinase inhibitors, or 'serpins,' including a tandem duplication of the squamous cell carcinoma antigen (SCCA) gene and 2 other members of the ovalbumin family of serine proteinase inhibitors, plasminogen activator inhibitor type 2 and maspin (protease inhibitor-5). Schneider et al. (1995) presented evidence that the neutral and acidic forms of SCCA are encoded by SCCA1 and SCCA2, respectively.