The purpose of this study was to investigate the expression of sarcosine metabolism-related proteins according to thyroid cancer subtypes and the implications of these findings. We performed tissue microarrays of 557 thyroid cancer cases (papillary thyroid carcinoma [PTC]: 344, follicular carcinoma [FC]: 112, medullary carcinoma [MC]: 70, poorly differentiated carcinoma [PDC]: 23, and anaplastic carcinoma [AC]: 8) and 152 follicular adenoma cases. Immunohistochemical staining for sarcosine metabolism-related molecules [glycine N-methyltransferase (GNMT), sarcosine dehydrogenase (SARDH), and l-pipecolic acid oxidase (PIPOX)] was conducted, and the results were analyzed based on clinicopathologic parameters. Results: The expression of SARDH and PIPOX was different depending on thyroid cancer subtypes. PTC showed higher expression than other subtypes (P<0.001). Among PTC, follicular variant (FV) showed lower expression than conventional type (P = 0.010 and P<0.001) and PTC with BRAF V600E mutation showed higher expression than PTC without BRAF V600E mutation (P<0.001). In univariate analysis, PIPOX positivity was associated with shorter overall survival (OS) in PTC (P = 0.024). In conclusion, the expression of sarcosine metabolism-related proteins varied according to thyroid cancer subtypes. SARDH and PIPOX showed higher expression in PTC; among PTC, FVPTC showed lower expression and PTC with BRAF V600E mutation showed higher expression
