In this study, we aim to retrospectively measure the levels of DNA repair proteins (MSH2, MLH1, and MGMT) from representative blocks of tissue material in patients with a confirmed diagnosis of papillary thyroid carcinoma, chronic thyroiditis, or nodular colloidal goiter by thyroidectomy and to examine the clinical predictive effect of these levels. Here, MSH2 is linked to Hashimoto thyroiditis.