A Genomic Score to Predict Local Control among Patients with Brain Metastases Managed with Radiation.

PURPOSE/OBJECTIVE(S): Clinical predictors of local recurrence following radiation among patients with brain metastases (BrM) provide limited explanatory power. As a result, radiation doses and fractionation schemes are relatively homogeneous and prescribed with a "one-size-fits-all" approach. We hypothesized that tumor-specific genomic alterations may underlie radiation sensitivity among patients with BrM and sought to develop a DNA-based signature of radiation-based efficacy in this patient population, utilizing genes that are readily testable in modern-day assays, to identify subpopulations at greater vs. lesser risk of recurrence.MATERIALS/METHODS: We identified 570 patients with 1,487 distinct BrM managed with whole-brain (WBRT) or stereotactic radiation therapy (SRS/SRT) at a tertiary cancer center (2013-2020) for whom next-generation sequencing panel data (OncoPanel, 239 genes) were available on at least one extracranial or intracranial tumor specimen. Fine/Gray's competing risks regression was utilized to compare local recurrence on a per-metastasis level among patients with vs. without somatic alterations of likely biological significance across 84 OncoPanel genes with a mutational frequency of >0.5%. Genes with a q-value<0.10 were utilized to develop a numeric "Brain-Radiation Prediction Score" ("Brain-RPS") to quantify local recurrence risk.RESULTS: Genomic alterations of potential biological relevance in 11 (ATM, MYCL, PALB2, FAS, PRDM1, PAX5, CDKN1B, EZH2, NBN, DIS3, MDM4) and two genes (FBXW7 and AURKA) were associated with a decreased or increased risk of local recurrence, respectively (q-value<0.10). Weighted scores corresponding to the strength of association with local failure for each gene were summed to calculate a patient-level Brain-RPS. On multivariable Fine/Gray's competing risks regression, Brain-RPS [1.66 (1.44-1.92, p<0.001)], metastasis-associated edema [1.89 (1.38-2.59), p<0.001], and receipt of WBRT without SRS/SRT or neurosurgical resection [2.73 (1.78-4.20), p<0.001] were independent predictors of local failure.CONCLUSION: Utilizing a targeted panel of genes with a known role in cancer pathogenesis, we developed a genomic score that can be calculated from an extracranial or intracranial site to quantify local recurrence risk following brain-directed radiation. Prior attempts to develop a biomarker-based radiation response signature have not focused on patients with BrM and have primarily relied on RNA-based measures of radiosensitivity, limiting their utility in real-world clinical practice for this patient population. To our knowledge, this represents the first study to systemically correlate DNA-based alterations with radiation-based outcomes among patients with BrM. If validated, Brain-RPS has potential to facilitate clinical trials aimed at genome-based personalization of radiation treatment among patients with BrM.