MON-568 Differences in Ultrasound Characteristics, Molecular Analysis, and Management of Indeterminate Thyroid Nodules (ITN) in Older vs. Younger Patients

Introduction Thyroid nodules (TN) are common and the prevalence increases with age, however, 95% are benign. Fine-needle aspiration (FNA) is the gold standard to evaluate TN. We previously demonstrated the rate of surgery was significantly lower in the older (O) vs. younger (Y) patients in the subgroup of benign (6.5% vs. 15.7%, P < 0.01) disease. This study will determine if indeterminate TN (ITN) in the O vs. Y patients have differences in ultrasound (US) features, molecular studies and surgical management. Methods 1402 sequential TN (greater than 1 cm) were biopsied from January 2015 - December 2016. Demographic data, US characteristics, molecular studies and pathology results were compared between older ≥ 65 year-old (O) and the younger < 65 year-old (Y) patients. Results/ Discussion The 442 (31.5%) ITN (Bethesda 3, 4, 5) were included in this study. There were 101 patients (22.8%) older than 65 years. The mean age was 72.0 ± 5.6 vs. 47.0 ± 11.4 years in the O and Y groups. There was no difference in gender or TN size (2.6 ± 1.2 vs. 2.6 ± 1.3 cm, P=0.40) between the groups. The O group had less Hispanic patients (10.9% vs. 23.8%, P=0.04) and more multinodular glands (81.4% vs. 67.0%, P=0.01) compared to the Y group. ThyroSeq V.2 molecular test was performed in 96.8% of ITN. Rates of positive mutations were similar (37.6% vs. 34.6%, P=0.86) but the high risk mutations were less common in the O vs. Y group (42.1% vs. 72.9%, P< 0.01). Surgery was performed in 159 (36.0%) ITN. Surgery rates of ITN were lower in the O vs. Y group (27.7% vs 38.4%, P= 0.05). Surgical pathology of all ITN showed benign 57.8%, malignancy 24.7%, and NIFTP 9.2%. Pathology was not different in both groups (P=0.36). Although malignancy occurred in 42.9% vs. 29.8%, P=0.18, in the O vs. Y groups, the difference was not significant. Suspicious US characteristics were not affected by age group (P= 0.66). The ITN with malignant pathology was significantly associated with Bethesda 5 cytology, high risk mutations and US characteristics including hypoechogenicity, undulating/ lobulated/ infiltrative margins, micro-, macrocalcification, and high intranodular blood flow (P< 0.01). In the O group, ITN with malignant pathology was not associated with microcalcification but was associated with hypoechogenicity, abnormal margins, macrocalcification and vascular flow. Conclusions Among ITN in the elderly of our cohort, the frequency of high risk molecular mutations and the surgical rates were lower than in the young adults. The typical high risk US characteristics associated with malignancy can be used to guide the practical ITN management combined with FNA results and molecular studies in the elderly. This study suggests differences in pathology and management of ITN between older and younger patients.