Correlation between Histopathological Prognostic Tumor Characteristics and [¹⁸F]FDG Uptake in Corresponding Metastases in Newly Diagnosed Metastatic Breast Cancer

Background: In metastatic breast cancer (MBC), [F-18]fluorodeoxyglucose positron emission tomography/computed tomography ([F-18]FDG-PET/CT) can be used for staging. We evaluated the correlation between BC histopathological characteristics and [F-18]FDG uptake in corresponding metastases. Patients and Methods: Patients with non-rapidly progressive MBC of all subtypes prospectively underwent a baseline histological metastasis biopsy and [F-18]FDG-PET. Biopsies were assessed for estrogen, progesterone, and human epidermal growth factor receptor 2 (ER, PR, HER2); Ki -67; and histological subtype. [F-18]FDG uptake was expressed as maximum standardized uptake value (SUVmax) and results were expressed as geometric means. Results: Of 200 patients, 188 had evaluable metastasis biopsies, and 182 of these contained tumor. HER2 positivity and Ki -67 >= 20% were correlated with higher [F-18]FDG uptake (estimated geometric mean SUVmax 10.0 and 8.8, respectively; p = 0.0064 and p = 0.014). [F-18]FDG uptake was lowest in ER-positive/HER2negative BC and highest in HER2-positive BC (geometric mean SUVmax 6.8 and 10.0, respectively; p = 0.0058). Although [F-18]FDG uptake was lower in invasive lobular carcinoma (n = 31) than invasive carcinoma NST (n = 146) (estimated geometric mean SUV(max )5.8 versus 7.8; p = 0.014), the metastasis detection rate was similar. Conclusions: [F-18]FDG-PET is a powerful tool to detect metastases, including invasive lobular carcinoma. Although BC histopathological characteristics are related to [F-18]FDG uptake, [F-18]FDG-PET and biopsy remain complementary in MBC staging (NCT01957332).