Correlation of breast cancer subtypes, based on estrogen receptor, progesterone receptor, and HER2, with functional imaging parameters from 68Ga-RGD PET/CT and 18F-FDG PET/CT

Purpose Imaging biomarkers from functional imaging modalities were assessed as potential surrogate markers of disease status. Specifically, in this prospective study, we investigated the relationships between functional imaging parameters and histological prognostic factors and breast cancer subtypes. Methods In total, 43 patients with large or locally advanced invasive ductal carcinoma (IDC) were analyzed (47.6 +/- 7.5 years old). Ga-68-Labeled arginine-glycine-aspartic acid (RGD) and F-18-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) were performed. The maximum and average standardized uptake values (SUVmax and SUVavg) from RGD PET/CT and SUVmax and SUVavg from FDG PET/CT were the imaging parameters used. For histological prognostic factors, estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) expression was identified using immunohistochemistry (IHC) or fluorescent in situ hybridization (FISH). Four breast cancer subtypes, based on ER/PR and HER2 expression (ER/PR+,Her2-, ER/PR+,Her2+, ER/PR-,Her2+, and ER/PR-,Her2-), were considered. Results Quantitative FDG PET parameters were significantly higher in the ER-negative group (15.88 +/- 8.73 vs 10.48 +/- 6.01, p = 0.02 for SUVmax; 9.40 +/- 5.19 vs 5.92 +/- 4.09, p = 0.02 for SUVavg) and the PR-negative group (8.37 +/- 4.94 vs 4.79 +/- 3.93, p = 0.03 for SUVavg). Quantitative RGD PET parameters were significantly higher in the HER2-positive group (2.42 +/- 0.59 vs 2.90 +/- 0.75, p = 0.04 for SUVmax; 1.60 +/- 0.38 vs 1.95 +/- 0.53, p = 0.04 for SUVavg) and showed a significant positive correlation with the HER2/CEP17 ratio (r = 0.38, p = 0.03 for SUVmax and r = 0.46, p < 0.01 for SUVavg). FDG PET parameters showed significantly higher values in the ER/PR-,Her2- subgroup versus the ER/PR+,Her2- or ER/PR+,Her2+ subgroups, while RGD PET parameters showed significantly lower values in the ER/PR-,Her2- subgroup versus the other subgroups. There was no correlation between FDG and RGD PET parameters in the overall group. Only the ER/PR-,Her2- subgroup showed a significant positive correlation between FDG and RGD PET parameters (r = 0.59, p = 0.03 for SUVmax). Conclusion Ga-68-RGD and F-18-FDG PET/CT are promising functional imaging modalities for predicting biomarkers and molecular phenotypes in breast cancer patients.