PSAT378 Hashimoto's Thyroiditis and Differentiated Thyroid Cancer Aggressiveness

Abstract

Abstract Background Hashimoto's thyroiditis (HT) is associated with a 1.5-fold increased risk of differentiated thyroid cancer (DTC). It is postulated that the inflammatory milieu in HT may damage thyrocytes, increasing the risk of cancer. However, it is not precisely known how the presence of thyroiditis affects aggressiveness of DTC and if a causal relationship exists. It has been suggested HT may correlate with a less aggressive phenotype with smaller tumor size, lower rate of aggressive variants, less frequent radioactive-iodine administration, and higher rates of clinical remission. The aim of this study was to investigate the pathological features of DTC in patients with HT and whether length of time with HT affects tumor aggression. Method Charts of 367 consecutive patients with DTC undergoing thyroidectomy were reviewed. Clinical and pathological factors were analyzed. A composite score of tumor aggressiveness was calculated using the presence of multifocality, angioinvasion, lymphatic invasion, extrathyroidal extension, central and lateral lymph node (LLN) involvement. This score and tumor size were compared in patients with clinical (elevated thyroid peroxidase or anti-thyroglobulin antibodies) or pathological (presence of inflammation on pathology) HT. Time to surgery from diagnosis of HT was also evaluated. Results In 367 patients with DTC (343 papillary, 29 follicular, 5 both), mean size of the largest tumor was 1.5±1.7cm, mean composite score was 1.3±1.6cm. Seventy-three (19.9%) and 156 (42.5%) patients had clinical or pathological HT, respectively; 92 (25.1%) had preoperative hypothyroidism. Patients with clinical HT alone, or in addition to pathological HT, had a reduced risk of LLN disease (Odds Ratio: 0.21 p<0.005, and OR: 0.43 p=0.01, respectively); those with pathological HT alone had a trend towards lower risk (p=0.06). Neither the overall score for tumor aggressiveness nor tumor size correlated with clinical or pathological HT. Length of time from diagnosis of clinical HT to surgery was not associated with tumor size, aggressiveness or presence of inflammation on pathology. Conclusion Clinical HT is associated with reduced risk for LLN metastasis, supporting the suggestion that presence of HT confers a better prognosis in DTC. Length of time with HT does not alter the risk for aggressive features of DTC indicating lack of an escalating causal relationship. Presentation: Saturday, June 11, 2022 1:00 p.m. - 3:00 p.m.