Prognostic value of prognostic nutritional index in breast cancer patients receiving neoadjuvant therapy: a systematic review and meta-analysis

Objective: Although the prognostic utility of the prognostic nutritional index (PNI) in breast cancer (BC) treated with neoadjuvant chemotherapy (NACT) has been widely reported, the available evidence remains inconsistent. Therefore, this meta-analysis systematically evaluated the predictive value of pre-NACT PNI for clinical outcomes in patients with BC. Methods: PubMed, Embase, Web of Science, and the Cochrane Library were queried comprehensively through November 2025 to identify reports evaluating the association of pre-NACT PNI with overall survival (OS), disease-free survival (DFS), and pathological complete response (pCR) in individuals with BC. Eligible studies were selected according to the PICOS framework. Hazard ratios (HRs) and odds ratios (ORs), along with 95% confidence intervals (CIs), were retrieved. Effect estimates were synthesized using fixed-or random-effects models as indicated, and robustness was tested by subgroup analyses, sensitivity analyses, and evaluation of publication bias. Results: Nine studies comprising 3,718 patients were included. A high pre-treatment PNI was significantly associated with better OS (HR = 0.36, 95% CI 0.25-0.52; p < 0.001) and increased odds of achieving pCR (OR = 1.90, 95% CI 1.21-2.98; p = 0.005). A favorable association was also observed for DFS (HR = 0.52, 95% CI 0.31-0.87; p = 0.01); however, this finding should be interpreted with caution because substantial heterogeneity was present and the estimate showed limited stability in leave-one-out sensitivity analyses. Subgroup analyses indicated that sample size, age, PNI cut-off value, and geographic region might modify the predictive performance of PNI for DFS and pCR. Conclusions: A high pre-NACT PNI was significantly associated with longer OS and a higher likelihood of pCR in patients with BC receiving NACT. A favorable association with DFS was also observed, but this finding should be interpreted cautiously because of substantial heterogeneity and limited robustness. PNI may serve as a simple and practical marker for clinical risk stratification, although further prospective validation is warranted. Systematic review registration: https://www.crd.york.ac.uk/prospero/, identifier CRD420251268856.