MON-547 Post-Surgically Discovered Differentiated Thyroid Microcarcinomas Are More Commonly Found in Patients eith Chronic Lymphocytic Thyroiditis Compared to Those with Multinodular Goiter or Graves' Disease

Introduction: Incidental finding of differentiated thyroid microcarcinomas (DTMc) in patients with thyroid nodules, undergoing thyroid surgery for benign indications, have become increasingly common. Even though carcinogenesis might relate to the background disease of the gland, the incidence of DTMc in the setting of various thyroid disorders remains unclear. We designed the present study to address this question. Methods/ Subjects: We reviewed the data from two prospectively collected databases of patients undergoing thyroid surgery in two high-volume tertiary care referral centers, one in the USA (A) and the other one in Greece (B) over 14 consecutive years. We collected data on the preoperative surgical indication, FNA cytology and surgical pathology. We excluded subjects operated for thyroid cancer or indications at high risk for malignancy (FNA suspicious for thyroid cancer, follicular neoplasm, suspicious for follicular neoplasm, FLUS/AUS, cellular specimen or sonographic features of malignancy), and those with post-surgical pathology consistent with PTC >9mm in largest diameter. We split our subjects based on pathology data in those with chronic lymphocytic thyroiditis (CLT), Graves disease (GR) or multinodular goiter (MNG). Incidence of DTMc or features of tumor aggressiveness were compared among groups, using Fischer’ s exact test and odds ratios (OR) were calculated. Categorical values were compared with Kruskal Wallis test. P values <0.05 were deemed significant. Results: We reviewed 6096 cases of thyroid surgery (A:2711, B:3385). We included 3909 subjects. Overall 609 (15.6%) DTMc were identified [A:256/2003 (12.8%), B:353/1906(18.5%) OR 0.79, p<0.0001]. CLT was present in 626 subjects; where DTMc was present in 155 (24.8%) [A:83/410 (20.2%), B: 72/216 (33.3%), OR 0.51 p<0.001]. GR was present in 377 subjects; where DTMc was present in 39 (10.3%) subjects [A:14/209 (6.7%) B: 25/168 (14.9%) OR 0.41, p=0.01]. MNG was present in 1964 subjects; where DTMc was present in 314 (15.9%) subjects [A: 58/686 (8.5%), B:256/1278 (20.0%)]. The incidence of DTMc was significantly higher in CLT compared to MNG (OR 1.73) or GR (OR 2.85) (p<0.001 for both) and in MNG compared to GR (OR 1.64, p=0.0064). Maximal tumor diameter was not significantly different among groups (CLT 0.46cm, MNG 0.44cm, GR 0.44cm, p=0.56). Conclusions: Incidentally discovered differentiated thyroid microcarcinomas are more commonly identified in surgical specimens from subjects with chronic lymphocytic thyroiditis as compared to patients with multinodular goiter, while patients with Graves' disease present with a much smaller incidence compared to both groups. This data supports previously published findings that euthyroid Hashimoto thyroiditis could allow for carcinogenesis, while Graves disease could have a protective role.