Prognostic value of baseline 18F-FDG PET/CT in first-line pembrolizumab plus chemotherapy for metastatic triple-negative breast cancer.

Abstract

e13111 Background: The treatment landscape of metastatic triple-negative breast cancer (mTNBC) is rapidly evolving. Pembrolizumab with chemotherapy has been the first-line standard; more recently, improved efficacy has been reported with sacituzumab govitecan. Therefore, biomarkers beyond PD-L1 CPS are urgently needed to better guide treatment selection. We aimed to evaluate the prognostic value of baseline 18F-FDG PET/CT in patients with mTNBC treated with first-line pembrolizumab and chemotherapy. Methods: This multinational, multicenter retrospective study was conducted within the CEBCC-101 real-world evidence project across 18 cancer centers. Female patients with histologically confirmed mTNBC who received first-line pembrolizumab combined with chemotherapy outside of clinical trials in Poland, the Czech Republic and Slovakia between September 2022 and June 2025 were included. Among 178 eligible patients, 53 underwent baseline 18F-FDG PET/CT. The highest tumor SUVmax was analyzed as a prognostic biomarker for progression-free survival (PFS) and overall survival (OS). Results: SUVmax, analyzed as a continuous variable, was significantly associated with PFS, with a 3.8% increase in the hazard of PFS event per 1-unit increase. The optimal SUVmax cut-off for PFS was 7.3 (sensitivity 0.95, specificity 0.44, AUC 0.70). Patients with SUVmax > 7.3 (highSUV) had significantly shorter PFS compared with those with SUVmax ≤7.3 (lowSUV) (median PFS 6.7 vs 16.1 months; HR 2.90; 95% CI 1.19–7.08; p = 0.019). Twelve-month PFS rates were 29.8% and 73.4%, respectively. HighSUV was also associated with inferior OS (HR 8.40; 95% CI 1.08–64.9; p = 0.042), with 2-year OS rates of 35.7% versus 83.3%. In multivariable analysis, SUVmax remained independently associated with inferior PFS and OS, irrespective of age, ECOG performance status, de novo versus recurrent disease, and metastatic site. Each 5-unit increase in SUV was associated with a higher risk of a PFS event (HR 1.35; 95% CI 1.10–1.66; p = 0.004) and with an increased risk of death (HR 1.60; 95% CI 1.13–2.28; p = 0.009). Conclusions: Baseline 18F-FDG PET/CT–derived SUVmax is a strong prognostic biomarker in patients with mTNBC treated with first-line pembrolizumab and chemotherapy. High SUVmax identifies a subgroup of patients with substantially poorer PFS and OS, and may help guide risk-adapted therapeutic strategies.