# Prognostic value of baseline FDG PET/CT in HER2-positive metastatic breast cancer treated with first-line trastuzumab, pertuzumab, and docetaxel

## TL;DR

This study shows that baseline FDG PET/CT scans can predict survival outcomes in patients with HER2-positive metastatic breast cancer treated with trastuzumab, pertuzumab, and docetaxel.

## Contribution

The study demonstrates that FDG PET/CT SUVmax is an independent prognostic biomarker for progression-free survival in HER2-positive metastatic breast cancer patients receiving first-line THP therapy.

## Key findings

- Higher SUVmax values (>9.6) were associated with significantly shorter progression-free survival (18.9 vs. 43.9 months).
- Low SUVmax (≤9.6), ER positivity, and oligometastatic disease were independent predictors of durable treatment benefit.
- 35% of patients achieved long-term response (PFS ≥35 months) with a median overall survival of 85.0 months.

## Abstract

Trastuzumab, pertuzumab, and docetaxel (THP) have represented the standard first-line treatment for HER2-positive metastatic breast cancer (MBC) for over a decade, following the pivotal CLEOPATRA trial. However, interim results from the DESTINY-Breast09 trial suggest that trastuzumab deruxtecan (T-DXd) may soon replace THP as the new first-line standard. Recent developments in treatment have raised new questions about how best to match therapy intensity with individual patient profiles. FDG PET/CT, routinely used for metabolic imaging, might help by identifying patients with differing prognoses based on baseline tumor activity. We investigated the prognostic relevance of baseline FDG PET/CT and its association with treatment outcomes in HER2-positive MBC patients receiving first-line THP.

We retrospectively analyzed 194 patients with HER2-positive MBC who underwent baseline FDG PET/CT within 12 months before initiating THP therapy (2017–2024). SUVmax was recorded, and optimal cut-off values for progression-free survival (PFS) was determined by ROC analysis. Cox regression and logistic regression were used to identify independent predictors of PFS, OS, and long-term response (PFS ≥ 35 months).

Median PFS was 29.1 months; 2-year PFS was 60.3%. SUVmax > 9.6 was associated with significantly shorter PFS (18.9 vs. 43.9 months; p = 0.002) and remained independently prognostic in multivariate analysis (HR 1.98; p = 0.001). Median OS was 85.0 months. Among 162 evaluable patients, 35% were classified as long responders. ER positivity (OR 4.82), oligometastatic disease (OR 2.60), and low SUVmax (≤ 9.6; OR 2.78) were independent predictors of durable benefit.

Baseline SUVmax derived from FDG PET/CT is an independent predictor of PFS in HER2-positive MBC treated with first-line THP. Integration of metabolic imaging biomarkers with clinical and molecular factors may support more personalized treatment approaches in this evolving therapeutic setting.

The online version contains supplementary material available at 10.1186/s13058-025-02191-7.