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

Background: In metastatic breast cancer (MBC), [ ¹⁸ F]fluorodeoxyglucose positron emission tomography/computed tomography ([ ¹⁸ F]FDG-PET/CT) can be used for staging. We evaluated the correlation between BC histopathological characteristics and [ ¹⁸ F]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 [ ¹⁸ F]FDG-PET. Biopsies were assessed for estrogen, progesterone, and human epidermal growth factor receptor 2 (ER, PR, HER2); Ki-67; and histological subtype. [ ¹⁸ F]FDG uptake was expressed as maximum standardized uptake value (SUV _max ) 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 [ ¹⁸ F]FDG uptake (estimated geometric mean SUV _max 10.0 and 8.8, respectively; p = 0.0064 and p = 0.014). [ ¹⁸ F]FDG uptake was lowest in ER-positive/HER2-negative BC and highest in HER2-positive BC (geometric mean SUV _max 6.8 and 10.0, respectively; p = 0.0058). Although [ ¹⁸ F]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: [ ¹⁸ F]FDG-PET is a powerful tool to detect metastases, including invasive lobular carcinoma. Although BC histopathological characteristics are related to [ ¹⁸ F]FDG uptake, [ ¹⁸ F]FDG-PET and biopsy remain complementary in MBC staging (NCT01957332).