ODP495 Medullary Thyroid Cancer Outcome in a Tertiary Care Centre in Atlantic Canada

Abstract Background Medullary thyroid carcinoma (MTC) constitutes around 1-2% of all thyroid cancer with a paucity of published data. Distinctively, MTC has a strong genetic component with oncogene mutations. For AJCC stages I, II, III, and IV, 5-year overall survival (OS) rates are 100, 90, 86.5 and 55.5%. The aims of this study are to report outcomes of the MTC patient cohort managed at a single tertiary cancer centre and specifically that of the subset of patients who have a biochemically incomplete response to primary surgical management. Objectives Explore the incidence and outcome of MTC including demographics, stage, genetic mutation status, dynamic risk stratification (DRS), and OS rate. Compare the outcome of MTC patients found to have low detectable post-op calcitonin (POC) levels (10-200 pg/ml=Grp B)) with those who have undetectable (< 10 pg/ml=Grp A) and significantly high-level POC levels (>200 pg/ml=Grp C). Methods Patients with MTC were identified from the Interdisciplinary Thyroid Oncology Clinic (ITOC) prospective database. Data was extracted and completed with a chart review. Results 35 cases with MTC were identified from 1570 cases. 21/35 were males. The diagnosis was made between 1988 and 2019 with a median age at diagnosis of 50 years (range=15 to 77) and a median follow-up of 8 years. Distribution (and 5-year OS, p=0.515) across Stages I, II, III, IV were 23% (100%), 14% (100%), 17% (100%) and 32% (90%) respectively with 14% unknown. 10 (29%) tested positive for RET gene mutations. Post-operative DRS response to initial treatment for 29 cases found 48%, 35%, and 17% were classified into excellent (E=undetectable calcitonin), biochemical incomplete (B=only detectable calcitonin), or structural incomplete (S=structural disease present) respectively. The 29 cases with available POC and DRS were divided into Groups A, B, and C based on POC levels as above. The final status at last follow up for Grp A was 13/14 (93%) with E and 1 (7%) with S, for Grp B 6/9 (67%) with B, 3/9 (33%) with S, and for Grp C 6/6 (100%) with S. The DRS for Grp A, B and C was 100% E, 89% B and 11% S, and 33% B and 67% S. The 5-year OS for Grp A, B, C was 100%, 89%, 100% (p=0.223) respectively. Conclusion This cohort of MTC cases failed to show significant differences in OS by stage and POC levels but did exhibit a higher rate of genetic mutations (29%) than those from other regions of Canada. Additionally, a biochemically incomplete response with a POC level above 200 pg/ml was highly suggestive of progressive structural disease as final outcome. This study will provide the template for a national survey of MTC in Canada facilitating analysis of a larger dataset. Presentation: No date and time listed