Squamous cell carcinoma (SCC) is a malignant tumor of squamous epithelium. Squamous epithelial cells are the main part of the epidermis, but are also present in the lining of the digestive tract, lungs, and other areas of the body. SCC occurs as a form of cancer in diverse tissues, mainly the lung, uterine cervix, vagina as well as lips, mouth and esophagus. Despite having the same name, squamous cell carcinoma, the SCCs of different locations show tremendous differences in their presenting symptoms, prognosis and response to treatment. Squamous cell carcinoma antigen (SCCA) is a subfraction of TA‑4, a tumor antigen first described by Kato and Torigoe in 1977. TA‑4, obtained from squamous cell carcinoma tissue of the uterine cervix, has been characterized as a glycoprotein with a molecular weight of 48 kDa and consists of at least 14 subfractions. SCCA being one of those subfractions, is a glycoprotein with a molecular weight of 42 kDa which can be detected by immunohistochemistry in the squamous tissue of the lung, vulva, exocervix, esophagus and skin. The respective gene for SCCA encodes two antigens, the neutral SCCA1 and the acidic SCCA2 which can be detected in serum. The biological function of SCCA is that of an enzyme inhibitor, where SCCA1 is an inhibitor of papain - like cysteine proteases (cathepsins L, S and K) and SCCA2 inhibits chymotrypsin - like serine proteases, cathepsin G and chymase.