Association of PET/CT-Derived Metabolic Parameters with Pathological Complete Response After Neoadjuvant Systemic Therapy in Breast Cancer: An Analysis Across Molecular Subtypes.

Background: Pathological complete response (pCR) following neoadjuvant systemic therapy (NST) is associated with improved outcomes in breast cancer. We evaluated the association between PET/CT-derived metabolic parameters and pCR and explored whether these associations differed according to molecular subtype. Methods: This retrospective study included 162 patients with stage II-III breast cancer who received NST followed by surgery and underwent 18F-FDG PET/CT at baseline and after completion of NST before surgery. Baseline SUVmax, post-treatment SUVmax, and percentage change in SUVmax (ΔSUVmax) were assessed for the primary tumor and axillary lymph nodes. Multivariable logistic regression and model performance analyses were performed. Results: Sixty-three patients (38.9%) achieved pCR. Higher ΔPrimary Tumor SUVmax and lower post-treatment primary tumor SUVmax were independently associated with pCR in separate multivariable models. The corresponding model AUCs were 0.837 and 0.848. Addition of PET-derived parameters to clinical-only models increased the AUC by 0.101 and 0.132, respectively (DeLong p = 0.001 and p < 0.001). No significant interaction was observed between ΔPrimary Tumor SUVmax and molecular subtype; in exploratory subgroup analyses, the association reached statistical significance in the HER2-positive subgroup only. Conclusions: PET/CT-derived metabolic parameters were independently associated with pCR and provided additional discriminatory information beyond clinicopathological factors. No significant interaction with molecular subtype was observed.