Systemic immune-inflammation and response indices is associated with early but not long-term survival after primary stereotactic radiosurgery for brain metastases

PURPOSE: Systemic inflammation indices from complete blood count (CBC) have been proposed as prognostic biomarkers in cancer, but their ability to predict time-specific overall survival (OS) after stereotactic radiosurgery (SRS) for brain metastases remains unclear. We evaluated five inflammation-based indices-the systemic immune-inflammation index (SII), systemic inflammation response index (SIRI), neutrophil-to-lymphocyte ratio, platelet-to-lymphocyte ratio, and lymphocyte-to-monocyte ratio-for short-term time-specific mortality at defined intervals after SRS. METHODS: In this single-institution retrospective study, we analyzed 141 patients (216 metastases) who underwent primary SRS for brain metastases between 2018 and 2022. Inflammation indices were calculated from pre-SRS CBC. Logistic regression assessed all-cause mortality at 1, 3, 6, 12, and 24 months. Each index was tested in a separate multivariable model. Predictive performance was evaluated using receiver operating characteristic curves and bootstrapped area under the curve (AUC) values with 95% confidence intervals (CIs). RESULTS: Median age was 71 years (interquartile range (IQR) 62-76); 55% were male. Lung cancer was the most common primary (51%), followed by gastrointestinal (13%) and breast (11%) cancers. The median local tumor control duration was 10 months (IQR, 5-24). Median OS was 12 months (IQR 5-32); mortality rates were 12%, 21%, 31%, 52%, and 68% at 1, 3, 6, 12, and 24 months, respectively. SIRI showed the strongest association with 1-month mortality (AUC 0.74, 95% CI 0.56-0.88), while SII demonstrated the highest discriminative performance for 3-month (AUC 0.75, 95% CI 0.64-0.86) and 6-month (AUC 0.71, 95% CI 0.60-0.80) mortality. Although early mortality was predictable, no index demonstrated sustained discriminative accuracy for OS at 12 or 24 months. Cancer origin also influenced short-term and long-term outcomes. CONCLUSIONS: SII and SIRI are associated with early (within 6 months) but not long-term OS after SRS; however, their clinical utility remains exploratory and requires external validation.