This study aimed to evaluate the association between pretreatment [18F]FDG PET/CT-derived biomarkers and outcomes in metastatic breast cancer (mBC) patients treated with antibody-drug conjugates (ADCs) Sacituzumab Govitecan (SG) and Trastuzumab Deruxtecan (T-DXd).

A retrospective bicentric analysis was conducted on triple-negative mBC (mTNBC) patients treated with SG and HER2-low mBC patients treated with T-DXd, who underwent [18F]FDG PET/CT scans before therapy. Key biomarkers, including maximum standardized uptake value (SUVmax), total metabolic tumor volume (TMTV) and maximum tumor dissemination (Dmax), were measured. Their prognostic value for progression-free survival (PFS) and overall survival (OS) was assessed using Cox models and Kaplan-Meier curves.

128 patients were included: 71 mTNBC treated with SG and 57 HR-positive and -negative HER2-low mBC treated with T-DXd. Median follow-up was 12.9 months. In the SG cohort, median PFS and OS were 4.8 and 8.9 months, respectively. High Dmax (HR 2.1, 95% CI 1.1-4.3) and high TMTV (HR 2.9, 95% CI 1.2-6.6) were independently associated with shorter OS. In the T-DXd cohort, median PFS and OS were 5.8 and 9.0 months, respectively. High Dmax (HR 2.1, 95% CI 1.2-3.9) and high TMTV (HR 2.4, 95% CI 1.0-6.5) independently correlated with shorter PFS and shorter OS, respectively.

Pretreatment [18F]FDG PET/CT-derived biomarkers, namely TMTV and Dmax, have significant prognostic value in patients with mTNBC and HER2-low mBC treated with SG and T-DXd. These biomarkers improve prognostic prediction and may optimize treatment strategies, warranting their clinical use, but larger studies are needed to validate these findings.