8061 Factors Affecting Survival of Metastatic Medullary Thyroid Cancer: A Population-Based Study From Surveillance, Epidemiology, and End Results (SEER) Program

Abstract Disclosure: A. Abdelhameed: None. H. Ibrahim: None. M. Mortagy: None. Introduction: Medullary thyroid cancer (MTC) arises from parafollicular cells of the thyroid. 43% of patients with MTC have metastasis. It was shown that the overall 5-year survival of patients with MTC is 40.4%. The clinical course of MTC is highly variable. The Aim is to identify factors affecting survival of the metastatic MTC sub-population. Understanding these factors is important in treating these patients. Methods 340 patients: with metastatic MTC who were diagnosed from 1975 to 2020 were extracted from SEER after removing duplicates and those not diagnosed by positive histology or cytology. Survival analysis was conducted, and Kaplan-Meier graph was generated. Univariate Cox regression was performed for all variables and respective hazard ratios (HR) were produced. Multivariable cox regression was performed for statistically significant variables. Results: The cohort were 59% males with a median age of 60 years. Median survival for the cohort was 20 months with survival of 63%, 41% and 31% at 1, 3, and 5 years respectively. Univariate Cox regression was statistically significant for age (HR 1.02), brain metastasis (HR 2.70), liver metastasis (1.65), lung metastasis (1.42), not performing total thyroidectomy (HR 2.77), lymph node ratio (HR 2.45), and systemic therapy after surgery (HR 0.34). Univariate Cox regression was not statistically significant for sex, grade, radiotherapy, chemotherapy, treatment delay, bone metastasis, distant lymph node metastasis, multifocal cancer, total number of benign and malignant tumors, race/ethnicity, income, tumor size 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 age (HR 1.04), presence of lung metastasis (HR 1.91), and systemic therapy before surgery (HR 14.41). Conclusion: Increasing age, presence of lung metastasis and systemic therapy before surgery lead to worse prognosis in metastatic MTC. Gender, grade, radiotherapy, chemotherapy, treatment delay, bone or brain or liver metastasis, presence of multifocal cancer, race, tumor size and surgery don't affect survival according to multivariable cox regression. Future research is needed to study this group of patients. Presentation: 6/2/2024