Prognostic Value of Baseline Metabolic Tumor Volume on [18F]FDG PET/CT in Metastatic Breast Cancer Treated With CDK4/6 Inhibitors.

BACKGROUND

Cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) improve outcomes in hormone receptor-positive/human epidermal growth factor receptor 2-negative (HR+/HER2-) metastatic breast cancer (MBC), but predictive biomarkers are lacking. This study investigated the prognostic value of baseline total metabolic tumor volume (TMTV) for progression-free survival (PFS) and overall survival (OS).

MATERIALS AND

METHODS

This single-center, retrospective study analyzed 88 female patients with HR+/HER2- MBC treated with palbociclib or ribociclib. Baseline TMTV was calculated from 2-[¹⁸F]fluoro-2-deoxy-D-glucose ([¹⁸F]FDG) positron emission tomography/computed tomography (PET/CT) scans using LIFEx software by summing the metabolic tumor volume of all lesions (threshold: 40% of the maximum standardized uptake value [SUVmax]). The primary and secondary endpoints were PFS and OS, analyzed using Kaplan-Meier and Cox regression models. Statistical significance was set at P < .05.

RESULTS

The median PFS and OS were 19.4 and 45.4 months, respectively. A higher TMTV was significantly associated with increased risk of progression (P = .001). Patients with a TMTV below 163.3 mL had significantly longer median PFS (23.23 vs. 10.93 months; P = .007). For OS, a TMTV > 29 mL was an independent predictor of higher mortality, with a median OS of 22.76 months compared to 51.36 months (P = .002).

CONCLUSION

Baseline TMTV is an independent prognostic factor for both PFS and OS in patients with HR+/HER2- MBC treated with CDK4/6 inhibitors.