2873 - Stereotactic Radiosurgery for Spinal Metastases with Gastrointestinal Histology vs. Other Radioresistant Histologies

A. Pratapneni¹, D. Klebaner¹, J. A. Jaoude¹, T. Kollipara¹, K. A. Kumar Jr², E. Rahimy¹, I. C. Gibbs¹, M. G. Mendoza¹, A. Persad³, Y. Hori³, D. Park³, S. D. Chang³, K. N. Chou³, S. G. Soltys¹, and E. Pollom¹; ¹Department of Radiation Oncology, Stanford University School of Medicine, Stanford, CA, ²Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX, ³Department of Neurosurgery, Stanford University School of Medicine, Stanford, CA

Purpose/Objective(s): Gastrointestinal (GI) cancers, renal cell cancers (RCC), melanomas, and sarcomas are considered more radioresistant than other histologies. We analyzed institutional local failure outcomes of stereotactic radiosurgery (SRS) to spinal metastases from GI, RCC, melanoma, and sarcoma primaries with the hypothesis that GI primaries are associated with higher local failure (LF) rates than the other radioresistant primaries. Materials/

Methods: This retrospective analysis included patients with spine metastases of GI, RCC, melanoma, and sarcoma primaries treated with SRS at our institution between 2002 and 2022. Medians and interquartile ranges (IQR) were used to describe continuous variables including single-fraction equivalent dose (SFED) and minimum dose (Dmin) to GTV while percentages were used to describe categorical variables including presence or absence of epidural extension. We calculated the 1-year cumulative incidences of LF for each histology and used regression models to evaluate the effect of histology (GI vs non-GI primary) on LF using subdistribution hazard ratios (SHR) with death as a competing risk and controlling for SFED, Dmin, and epidural extension.

Results: We included 200 radioresistant spinal metastases in 120 patients (Table). Sarcoma histology was associated with lower 1-year LF than non-sarcoma histologies (3.3%, 95% CI 0.23%-15%, p = 0.02). 1-year LF rates for melanoma, GI, and RCC were 6.7% (95% CI 0.37%-27%, p = 0.73), 19% (95% CI 10%-29%, p = 0.41), and 22% (95% CI 14%-32%, p = 0.26), respectively. GI histology correlated with higher LF than the non-GI radioresistant histologies (adjusted SHR = 2.02, 95% CI 0.94-4.34, p = 0.072). Sarcoma histology was associated with lower LF than GI histology (adjusted SHR = 0.17, 95% CI 0.03-0.86, p = 0.03). In contrast, melanoma and RCC histologies did not have a statistically significant difference in LF rates than GI histology (adjusted SHR = 0.61, p = 0.57; and adjusted SHR = 0.72, p = 0.42, respectively).

Conclusion: Among radioresistant spine metastases, GI primaries had significantly higher rates of LF than non-GI primaries. These results may have been driven by lower LF rates of sarcoma primaries. These data suggest exploration of further SRS dose-escalation for GI spine metastases.

Abstract 2873 – Table 1

	RCC	Melanoma	Sarcoma	GI	p-value
N (%)	83 (41.5)	15 (7.5)	30 (15.0)	72 (36.0)
Prescription Dose, SFED (median [IQR])	18.0 [16.0-20.0]	16.4 [16.0-20.0]	18.2 [16.4-20.0]	18.0 [16.4-20.0]	0.23
Dmin, SFED (median [IQR])	17.1 [14.5-19.4]	20.0 [15.8-20.9]	17.7 [16.3-19.3]	17.1 [14.0-20.7]	0.62
Epidural Extension Bilsky > 0 (%)	40 (48.2)	8 (53.3)	8 (26.7)	27 (40.9)	0.26
1-year LF (% [95% CI])	22 [14-32]	6.7 [0.37-27]	3.3 [0.23-15]	19 [10-29]	0.11