The influence of immunohistochemistry-based subtypes on overall survival in breast cancer spine metastases: a systematic review and meta-analysis

Background Breast cancer spinal metastases present a growing clinical challenge, with survival outcomes varying significantly by immunohistochemistry-based subtype. Current prognostic models often overlook subtype-specific differences, potentially leading to suboptimal treatment decisions. This study aimed to establish the first comprehensive subtype-specific survival benchmarks for spinal metastases and to evaluate temporal trends in survival. Methods We conducted a systematic review and meta-analysis of survival outcomes following a predefined protocol (PROSPERO CRD42024580279). Eligible studies reported overall survival (OS) in patients with breast cancer spinal metastases, stratified by immunohistochemistry-based subtype: hormone receptor (HR +), human epidermal growth factor receptor 2-enriched (HER2 +), and triple-negative breast cancer (TNBC). Survival data were extracted from published figures with a digitizer program and then processed in R. The median OS was analyzed through pooled survival curves with 95% confidence intervals, compared via log-rank tests. To evaluate temporal trends, we performed era-stratified analyses (pre-2000, 2000–2019, post-2020) using chronological partitioning of study enrollment periods. Results After screening 2,348 records, we identified seven eligible cohorts comprising 672 patients. Analysis revealed significant survival differences among subtypes (log-rank p < 0.0001), with median OS of 28.9 months (95% CI 26.0–35.6; n = 347) for HR + , 43.7 months (31.9–48.7; n = 244) for HER2 + , and 10.7 months (8.9–19.2; n = 81) for TNBC (very low certainty of evidence for all outcomes). Temporal analysis of 4464 patients from 61 studies demonstrated significant survival improvements post-2020 (log-rank p < 0.0001). Conclusions This study establishes the first real-world unadjusted survival reference for subtypes in breast cancer spinal metastases, suggesting a potential survival advantage of HER2 + /HR + over HER2 + /HR − tumors. These findings underscore the essential role of subtyping in refining prognostic assessment for spinal metastases. Our findings demonstrate a temporal improvement in survival and highlight the persistent need for contemporary data in this rapidly evolving clinical landscape. Trial registration PROSPERO CRD42024580279.