Quantitative double-fluorescence immunohistochemistry (qDFIHC), a novel technology to assess protein expression: A pilot study analyzing 5-FU sensitive markers thymidylate synthase, dihydropyrimidine dehydrogenase and orotate phosphoribosyl transferases i

To evaluate the protein expression level in formalin-fixed cancer tissue specimens, the authors devised quantitative double-fluorescence immunohistochemistry (qDFIHC). Using this method, the 17 gastric cancer biopsy specimens, before undergoing S-1 based neoadjuvant chemotherapy, were assessed in order to determine the expression levels of the thymidylate synthase (TS), orotate phosphoribosyltransferase (OPRT) and dihydropyrimidine dehydrogenase (DPD) which determines S-1 efficacy. The ratios of OPRT/TS, OPRT/DPD and OPRT/(DPD + TS) which have been proposed to show a good correlation with S-1 efficacy, were calculated and compared with the clinical response. A significant difference was thus observed in OPRT/TS (P = 0.0049), OPRT/DPD (P = 0.0067) and OPRT/(DPD + TS) (P = 0.0013) between the responder and the non-responder groups. Therefore, the ratios assessed by qDFIHC may be a potentially effective predictor of the S-1 efficacy. Furthermore, qDFIHC may also be a useful method for assessing various protein levels in cancer tissues.