Squamous cell carcinoma arising in mature cystic teratoma of the ovary: an immunohistochemical analysis of its tumorigenesis

Aims:  Squamous cell carcinoma (SCC) is the most common form of malignant transformation in mature cystic teratoma (MCT) of the ovary. Some investigators have suggested the possibility of origin from columnar epithelium. The aim of this study was to analyse such tumours immunohistochemically to elucidate their histogenesis. Methods and results:  The expression of cytokeratin (CK) 10 and CK18 was examined in 21 samples of SCC arising in MCT. The expression of CK10 and CK18 was also assessed in SCCs arising in different organs (skin, vulva, lung and uterine cervix) for the purpose of comparison. SCC in MCT expressed CK10 in 7/21 cases [33.3%, 95% confidence interval (CI) 0.12–0.53] and CK18 in 14/21 cases (66.7%, 95% CI 0.46–0.87). SCC in MCT expressed CK10 less frequently, but CK18 more frequently, as is the case in SCCs of the uterine cervix (CK10, 20%; CK18, 70%) and the lung (CK10, 5%; CK18, 90%), both of which are derived from columnar epithelium by squamous metaplasia. Conclusions:  SCC in MCT may be derived from metaplastic squamous epithelium.