P2-09-06: Relevance of Breast Cancer Subtypes in Response Monitoring with 18F-FDG PET/CT during Neoadjuvant Chemotherapy.

Abstract

Abstract Background - Neoadjuvant chemotherapy (NAC) is increasingly applied in stage II and III breast cancer. Response monitoring with magnetic resonance imaging (MRI) has been shown valuable, but knowledge of the breast cancer subtype is essential for correct interpretation of response assessment.(Loo et al, J Clin Oncol 29:660–6, 2011) The aim of the present study was to evaluate the relevance of breast cancer subtype for 18F-fluorodeoxyglucose (FDG) positron emission tomography with computed tomography (PET/CT) markers for monitoring of therapy response during NAC. Methods - Evaluation included 94 women with primary stage II or III breast cancer and measurable (quantifiable) FDG tumor uptake. FDG PET/CT scans were performed before and after six weeks of NAC using similar prone patient positioning. FDG uptake of the primary tumor was quantified using maximum standardized uptake values (SUVmax). Tumors were divided into three subtypes using immunohistochemistry: human epidermal growth factor receptor 2 (HER2) positive, estrogen receptor (ER) positive/HER2 negative and triple negative. Tumor response was assessed as presence of residual tumor in the surgery specimen (no response or partial response) or absence thereof (near complete or complete response). Multivariate regression analysis and receiver operating characteristic (ROC) analyses were employed to determine significant associations. Results - A (near) complete response at pathology was observed in 16 (73%) of 22 HER2 positive tumors, 5 (12%) of 43 ER positive/HER2 negative tumors and 20 (69%) of 29 triple negative tumors. In the multivariate regression analysis for the whole group, (near) complete response in the surgery specimen was significantly associated with relative reduction of SUVmax of the tumor between both scans and breast cancer subtype (area under the curve of the ROC curve 0.88 [95% confidence interval 0.81−0.95], p<0.001); no significant associations were found for FDG uptake at baseline and age. In a subgroup analysis of breast cancer subtype, a significant association was found between pathologic response and relative reduction of SUVmax for ER positive/HER2 negative and triple negative tumors (p=0.012 and p<0.001, respectively), but not for HER2 positive tumors (p=0.151). Conclusion - Knowledge of the breast cancer subtype appears relevant for the assessment of response to NAC with FDG PET/CT. Response monitoring with FDG PET/CT may predict a pathological response adequately in ER positive/HER2 negative and triple negative tumors, but seems less accurate in HER2 positive tumors. The reasons for these differences need to be elucidated in further investigations. Disclosure - This study was performed within the framework of CTMM, the Center for Translational Molecular Medicine (www.ctmm.nl), project Breast CARE (grant 030–104). Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P2-09-06.