Squamous cell carcinoma antigen (SCC ag) is a group of glycoproteins with molecular weight ~45 kDa, belonging to the family of serine/cysteineprotease inhibitors. The protein was originally isolated by Kato and coworkers from human squamous cell carcinoma tissue and shown to consist of at least 10 subfractions differing in isoelectric point. More recent studies have shown that SCC antigen is composed of two distinct but highly homologous gene products, SCCA1 and SCCA2 with different inhibitor specificities.

SCC antigen is a serological marker of squamous cell carcinomas of the uterine cervix, vulva, lung, head & neck, and esophagus. In squamous cell carcinoma of the uterine cervix, pretreatment serum SCC ag may be used as an early stage prognostic factor7 and the use of pretreatment SCC ag has been suggested in order to select high-risk patients for adjuvant therapy4. Further, for patients with elevated levels of SCC ag before start of treatment, the profile of SCC ag correlates with the response to radio- and chemotherapy and measurement of SCC ag may thus be used for early detection of recurrent disease and to monitor the effect of therapy.