362P - Might Early Metabolic Response by 18F-FDG-PET/CT be Useful to Select Patients (PTS) With Breast Cancer (BC) who Will not Optimally Respond to Preoperative Chemotherapy (PCT)?

Abstract

ABSTRACT Purpose To evaluate 18F-2-fluoro-2-deoxy-D-glucose positron emission tomography/computed tomography (18F-FDG PET/CT) changes between baseline and after 2 cycles of PCT in pts with early/locally advanced (E/LA) BC, with the aim to verify whether early metabolic assessment of response during PCT may have a role in clinical practice to enable early changes in the therapeutic strategy. Patients and methods Sixty pts with newly diagnosed E/LA BC received 6-8 cycles of anthracycline and taxane-based PCT. Fifty-eight pts underwent surgery, which consisted in breast conserving surgery or radical mastectomy; axillary node dissection was performed in all cases. Optimal pathologic response (pR) to PCT was defined as absence of cancer cells in breast and ipsilateral axillary lymph nodes. All other conditions were defined as nonresponders (pNR). Maximum standardized uptake value (SUV max) with 18F-FDG PET/CT was measured for each pathologic lesion at baseline and after 2 cycles of PCT. SUV max percentage changes (Δ-SUV) were compared with pR rate according to immunohistochemical (IHC) BC characteristics. Δ-SUV >50% defined a metabolic response (MetR). Results Thirteen (22%) of 60 pts achieved pR. According to IHC, pR rates where 16% in ERpositive/HER2negative (ER + /HER2-) pts, 29% and 27% in HER2-positive (HER2+) and triple negative (TN) pts respectively. Sensitivity of metR to identify pR was 100% in all three subgroups, but the specificity was low: 38% in ER + /HER2- pts (38%) was the highest value. In this subgroup of pts PET had a low positive predictive value (24%), while the negative predictive value was 100%, showing, compared to HER2+ and TN pts, the highest ability to correctly predict pNR (32%). At a median follow-up of 36.6 months, recurrence rate was higher in metabolic non-responders, particularly in the ER + /HER2- subgroup, in which Kaplan-Meier analysis of disease-free survival confirmed a significant difference (p = 0.0490). Conclusions PET assay after 2 cycles of PCT correctly predicted pNR in 32% of ER + /HER2- pts, identifying a subgroup of BC pts with worse prognosis who might benefit from an early change of the therapeutic strategy. Disclosure All authors have declared no conflicts of interest.