2114 - Fifteen-Year Longitudinal Analysis of Spine Stereotactic Radiosurgery for Metastatic Thyroid Cancer

03:00pm - 04:00pm ET

Poster Hall - Exhibit Hall A

Screen: 14

POSTER

Presenter(s)

Ryan Ko, MD - MD Anderson Cancer Center, Houston, TX

R. B. Ko¹, D. Boyce-Fappiano¹, S. Perni², C. Wang², T. Beckham², M. C. Tom², J. P. Reddy³, D. N. Yeboa², M. F. F. McAleer², J. Li², M. E. Cabanillas⁴, N. L. Busaidy⁴, B. Amini⁵, C. Tatsui⁶, L. D. Rhines⁶, T. M. Briere⁷, A. J. Ghia², and B. De²; ¹MD Anderson Cancer Center, Department of Radiation Oncology, Houston, TX, ²Department of CNS Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, ³Department of Radiation Oncology, University of Texas MD Anderson Cancer Center, Houston, TX, ⁴Department of Endocrine Neoplasia & Hormonal Disorders, University of Texas MD Anderson Cancer Center, Houston, TX, ⁵Department of Musculoskeletal Imaging, The University of Texas MD Anderson Cancer Center, Houston, TX, ⁶Department of Neurosurgery, The University of Texas MD Anderson Cancer Center, Houston, TX, ⁷Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX

Purpose/Objective(s):

Metastatic thyroid cancer often follows an indolent course, resulting in prolonged survival that necessitates exceptionally durable local control (LC) for spinal metastases. While spine stereotactic radiosurgery (SSRS) is standard of care, data on long-term outcomes are sparse. This study presents a 15-year longitudinal analysis—the longest reported to date—to evaluate the sustained efficacy and safety of SSRS in this patient population.

Materials/Methods:

We retrospectively evaluated data on 80 patients (158 lesions) with spine metastatic thyroid cancer treated with SSRS at a single institution from 2004-2025. LC was assessed via post-treatment imaging. Multivariate analysis (MVA) evaluated predictors of LC including dose and fractionation regimens (range: 16-40 Gy in 1-5 fractions; BED10 28.8-81.6 Gy), MAPK mutation status (BRAF/RAS), and the presence of extra-spinal disease at the time of SSRS. Overall survival (OS) was stratified by presence of extra-spinal disease at time of SSRS. Median follow-up was calculated using reverse Kaplan-Meier method.

Results:

The median follow-up was 127 months (95% CI: 108–149). Histology distribution included 41% follicular, 34% papillary, 13% Hurthle cell, 9% medullary, and 4% anaplastic. The 1-, 3-, 5-, 10-, and 15-year LC rates were 97.1%, 86.0%, 79.2%, 74.0%, and 56.9%, respectively; median LC was not reached. The 1-, 3-, 5-, 10-, and 15-year overall survival (OS) rates were 79.4%, 48.8%, 34.4%, 14.7%, and 10.1%, respectively, with median OS of 35 months. On MVA, neither BED10 (p = 0.71) nor MAPK status (p = 0.19) was associated with LC. Extra-spinal disease was a major predictor of shorter OS (HR 4.91, p = 0.0019) but did not impact LC durability (p = 0.77). Grade 3 vertebral compression fractures (VCFs) occurred in 4 treated lesions (2.5%); notably, none occurred in the cohort with the highest BED10 dose prescription (24 Gy/1 fraction), and the majority were associated with pre-existing structural compromise or tumor progression. Grade = 3 esophageal toxicities occurred exclusively in two patients (2.5%) who received re-irradiation.

Conclusion:

SSRS provides durable local control for thyroid spinal metastases that can persist for over a decade, independent of mutation status or systemic disease burden. Overall prognosis is primarily dictated by extra-spinal disease burden (HR 4.91). High-grade VCFs are rare and likely driven by mechanical instability or disease progression rather than radiation intensity. High-grade esophageal toxicity was limited to salvage re-irradiation. Therefore, SSRS should be considered a primary strategy for durable local control in carefully selected patients given the potential for long-term survival.