Thymidylate synthase (TS) immunostaining in the diagnosis of the myoepithelial cells, basal cells, stratified epithelium cells, and associated tumors

BACKGROUND: Thymidylate synthase (TS) is an important prognostic biomarker for resistance to 5FU-based adjuvant chemotherapy. Recently, we found that TS was specifically expressed in the nucleus of the myoepithelial cell (MEC), basal cell (BC), transitional epithelial cell (TEC), squamous epithelial cell (SEC), and associated tumor using immunostaining. This prompted us to examine whether TS could be used as a diagnostic biomarker for MEC, BC, TEC, SEC, and associated tumors. METHODS: Formalin-fixed, paraffin-embedded specimens from 186 cases of tumors were immunostaining for expression of TS and p63. The diagnostic capability of TS as a reliable diagnostic marker was evaluated and compared with the expression of p63. RESULTS: TS exhibited a strong specific and stable nuclear immunoreactivity in all specimens including MEC, BC, TEC, and SEC when compared with p63. Notably, a variable degree of TS cytoplasmic positive immunoreactivity was observed in 58.3% of squamous-cell carcinoma (SQCC), 37.5% of basal cell carcinoma (BCC), 44.4% transitional-cell carcinomas (TCC), 41.7% mixed tumor (MT) and 56.5% of adenocarcinoma (ADC) specimens. CONCLUSIONS: In addition to being used as a strong prognostic factor for 5-FU resistance, TS also serves as a promising putative diagnostic marker for identifying MEC, BC, SEC, and TEC from GEC, and for distinguishing SQCC, BCC, TCC, and MT from ADC.