Abstract 4558: FDG-PET uptake in breast cancer molecular subtypes

Background: Data on breast cancer FDG uptake in relation to clinically relevant molecular subtypes and their interaction is scarce. Some have shown higher standardized uptake values (SUV) in triple negative (TN) and HER2+ than hormone receptor (HR)+ disease. We hypothesize that FDG uptake in HER2+ disease depends on HR status. Methods: We identified 186 invasive breast cancer patients with a whole body FDG-PET/CT scan between 2005 and 2010 at UCSF (within 6 months prior to or after diagnosis but before therapy). Receptor expression was assessed on adjuvant therapy naïve specimens using IHC (HR [ER and PR], HER2) and FISH (HER2) according to clinical practice. We related routinely assessed (log-transformed) SUVmax to receptor expression with linear regression and analysis of covariance (ANCOVA), and adjusted for tumor grade. Results: SUVmax was reported for 160 primary breast cancers and 154 had complete data for HR and HER2. Median age at diagnosis was 52 years (range 21-87), and 34% had localized, 52% regional, and 14% distant disease. Average tumor size was 3.9 cm (SD 2.2), and 12% had good, 51% moderate and 37% poor grade. FDG uptake strongly depended on molecular subtype (Table). Uptake was lowest in HER2-HR+ and somewhat - but not significantly - higher in HER2+HR- disease. The highest SUVmax was found in HER2+HR+, followed by TN disease (both significantly higher than HER2-HR+). The interaction between HR and HER2 in relation to FDG uptake was significant (P=0.003). ANCOVA showed that the higher TN uptake could largely be explained by differences in grade, whereas SUVmax in HER2+HR+ disease remained significantly higher than in HER2-HR+ disease. Conclusion: This large series of advanced primary breast cancer showed FDG uptake to be comparably low in HER2-HR+ and HER2+HR- disease, but significantly higher in HER2+HR+ and TN disease. Tumor grade largely explained the higher FDG uptake in TN disease but not the results for HER2+HR+. FDG-PET may need evaluation at different settings taking into account uptake variation due to tumor biology. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4558. doi:1538-7445.AM2012-4558