Stage-dependent performance and molecular subtype-specific relapse patterns on same-session [18F]FDG...

To evaluate stage-dependent performance of same-session [18F]FDG PET/contrast-enhanced CT (PET/ceCT) for initial breast cancer staging and PET/ceCT-detected relapse patterns during follow-up.

This retrospective single-centre study included a primary staging cohort with one index PET/ceCT per patient and a longitudinal cohort of follow-up/restaging examinations. PET/ceCT-derived endpoints were assessed against clinically adjudicated reference standards established through multidisciplinary team review, pathology when available and follow-up imaging. SUVmax and ceCT lesion diameter were analysed as exploratory biomarkers.

The staging cohort included 116 patients. Baseline stage was evaluable in 106 patients: 65 had cN-positive disease, 9 had cT3-4 cN0 disease and 32 had cT1-2 cN0 disease. Overall nodal staging performance showed sensitivity 64.8%, specificity 88.9%, PPV 92.0%, NPV 56.1% and accuracy 72.9%. In cT3-4 and/or cN-positive disease, PET-positive nodal findings had a PPV of 100%. Baseline M-stage assessment was limited by the low number of clinically confirmed M1 cases. SUVmax correlated with Ki-67 (rho = 0.322, p = 0.003, q = 0.022). The longitudinal cohort included 176 patients and 429 examinations. In 311 adjudicated examinations, restaging performance for disease progression showed sensitivity 100%, specificity 93.5%, PPV 97.3%, NPV 100% and accuracy 98.1%. First confirmed relapse was multiorgan/multisystem in 48/82 patients and visceral-only in 15/82; visceral conversion occurred in 5/16 patients with initial bone-only or nodal/locoregional relapse.

Same-session [18F]FDG PET/ceCT showed greatest baseline utility in higher-risk breast cancer and was useful for longitudinal characterization of relapse phenotype and metastatic evolution.