Predictive Impact of Pan-Immune Inflammation Value on Radiological Response in Metastatic Breast Cancer Patients on Palbociclib

Background: Hormone receptor–positive (HR+), HER2-negative metastatic breast cancer (MBC) is the most common subtype of advanced breast cancer. CDK4/6 inhibitors combined with endocrine therapy signicantly improve survival outcomes, but resistance frequently develops, emphasizing the need for reliable predictive biomarkers. The Pan-Immune Inammation Value (PIV), a composite index calculated from complete blood counts, reects systemic inammation and immune status. Although high PIV has been linked with poor prognosis across multiple cancers, its predictive role in radiological response to palbociclib-based therapy in HR+/HER2− MBC remains unexplored. We conducted a Methods: retrospective–prospective observational study at a tertiary cancer center in Bangalore, India, from 2019 to 2024. A total of 129 patients with HR+/HER2− MBC who received palbociclib with endocrine therapy were included. PIV was calculated as (neutrophils × platelets × monocytes) / lymphocytes. Radiological response was assessed at 6 months using RECIST v1.1. Statistical analyses included ANOVA to compare PIV values across response groups and receiver operating characteristic (ROC) analysis to establish an optimal cut-off. Baseline clinical and Results: treatment characteristics were similar between low and high PIV groups. At 6 months, the overall radiological outcomes were: complete response (CR) in 13.1%, partial response (PR) in 38.7%, stable disease (SD) in 28.6%, and progressive disease (PD) in 19.3%. Disease control (CR/PR/SD) was achieved in 54.2% of low PIV patients versus 26.3% of high PIV patients, while PD was more frequent in the high PIV group (13.1% vs. 6.2%; p < 0.001). Mean PIV values were lowest in CR (267.6) and progressively higher in PR (599.3), SD (601.4), and PD (1276.1) (p < 0.001). ROC analysis dened ≤530.8 as the optimal cut-off (AUC 0.702, 95% CI 0.615–0.779, sensitivity 76.1%, specicity 66.1%). Toxicity proles were consistent with previous CDK4/6 trials, with neutropenia (52.7% grade ≥3) as the most common adverse event. Baseline PIV is an Conclusion: inexpensive, reproducible, and clinically relevant biomarker that predicts radiological response to palbociclib in HR+/HER2− MBC. Integrating PIV into clinical practice may allow for improved patient stratication and personalized treatment strategies.