8080 Factors Affecting Survival of Lymph Node Positive Medullary Thyroid Cancer: A Population-Based Study From Surveillance, Epidemiology, and End Results (SEER) Program

Abstract Disclosure: M. Mortagy: None. A. Abdelhameed: None. M. Hegazy: None. Introduction: 50-70% of patients with MTC have positive lymph nodes. The Aim is to identify factors affecting survival of the lymph node positive MTC sub-population. Understanding these factors is important in treating these patients. Methods 1359 patients with lymph node positive MTC who were diagnosed with positive histology or cytology from 1975 to 2020 were extracted from SEER after removing duplicates. Survival analysis was performed, and Kaplan-Meier graph was produced. Univariate and multivariable Cox regression were performed, and respective hazard ratios (HR) were generated. Results: The cohort were 54% males with a median age of 55 years. Median survival: for the cohort was 163 months with survival of 91%, 80% and 74% at 1, 3, and 5 years respectively. Univariate Cox regression was statistically significant for age (HR 1.04), female sex (HR 0.64), T4 stage (HR 2.48), M1 stage (HR 5.43), bone metastasis (HR 4.74), brain metastasis (HR 17.1), liver metastasis (HR 5.41), lung metastasis (HR 5.97), distant lymph node metastasis (HR 6.00), number of positive lymph nodes (HR 1.008), lymph node ratio (HR 4.50), tumor size (HR 1.02), multifocal tumor (HR 0.69), total number of malignant tumors (HR 1.21), not performing total thyroidectomy (HR 6.35), chemotherapy (HR 3.85), radiotherapy after surgery (HR 1.67), beam radiotherapy (HR 2.20), systemic therapy after surgery (HR 0.67). Univariate Cox regression was not statistically significant for grade, treatment delay, total number of benign tumors, race/ethnicity, income, and living in rural areas. Multivariable cox regression was done after inclusion of all significant variables from univariate Cox regression. It was only significant for number of positive lymph nodes (HR 1.03), bone metastasis (HR 0.18), liver metastasis (HR 14.57), multifocal tumor (HR 3.49), total number of malignant tumors (HR 2.66), T4 stage (HR 3.57), M1 stage (HR 3.65), not performing total thyroidectomy (HR 352.43), tumor size (HR 1.03). Conclusion: Number of positive lymph nodes, T4 stage, M1 stage, presence of liver metastasis, presence of multifocal tumor, not performing total thyroidectomy and large tumor size lead to worse prognosis. Age, gender, chemotherapy, and lymph node ratio don’t affect survival. Future research is required to study this group of patients. Presentation: 6/2/2024