MON-550 Have New ATA Guidelines Changed the Diagnosis and Management of Thyroid Cancer? A Population-Based Study

Background : Thyroid cancer incidence is increasing in the United States, predominantly papillary thyroid cancer (PTC). Overdiagnosis of clinically indolent thyroid cancer contributes to the rise in incidence and adds to treatment and monitoring burdens. In March 2015, a symposium at the Endocrine Society introduced guidelines by the American Thyroid Association (ATA) for management of differentiated thyroid cancers (DTC).This included changes in recommendations for biopsy of sub-centimeter thyroid nodules and consideration of lobectomy for small, localized cancers. Objective : To identify how 2015 ATA guidelines on management of DTC have changed practice in a population-based study. Study Design : Population-based retrospective cohort study Methods : We utilized the Rochester Epidemiology Project (REP) database to identify all new cases of thyroid cancer in Olmsted County, MN between 2000 and 2017. We extracted information about demographics, mechanism of detection of the thyroid cancer, parameters of the tumor including pathologic type, size, and invasiveness, and initial management approach. Clinically relevant cancers were identified as those with aggressive histology (anaplastic, medullary, undifferentiated, Hurthle cell) or AJCC 8 Stage 3-4 differentiated thyroid cancers. Results: Between 2000 and 2017, a total of 313 new cases of thyroid cancer were diagnosed in Olmsted County, of which 249 were prior to March 1, 2015, and 64 thereafter. The cohort had a mean age of 46.5 years (SD 15.1), 70% female, predominantly Caucasian (87%), and 94% with PTC. Patients diagnosed before and after the index date had similar distributions of thyroid cancer histology, mean tumor size, mechanism of detection, and frequency of clinically relevant cancers. The percentage of thyroid cancers ≤ 1cm was reduced after the index date, but this was not significant (27% vs 37%, p=0.15). In patients with both ≤ 1cm PTC and ≤ 4cm PTC, there was a significant increase towards less intensive management (lobectomy, active surveillance, ethanol ablation) compared to complete thyroidectomy (total, near total, subtotal) (≤ 1cm: 22% vs 47%, p=0.04; ≤4cm: 13% vs 26%, p=0.01). Conclusion: In our study, we find that changes in ATA guidelines have not yet led to changes to changes in parameters of newly detected thyroid cancers in our population based study. However, there has been a significant trend towards less invasive management of microPTC and ≤ 4cm PTC, though there are still many patients having complete thyroidectomies with microPTC. Further studies will need to include how changes in management will impact outcomes of cancer recurrence, costs and burdens of follow-up care and patient’s quality of life.