PurposeOncotype DX, a 21-gene expression assay, provides a recurrence score (RS) which predicts prognosis and the benefit from adjuvant chemotherapy in patients with early-stage, estrogen receptor-positive (ER-positive), and human epidermal growth factor receptor 2-negative (HER2-negative) invasive breast cancer. However, Oncotype DX tests are expensive and not readily available in all institutions. The purpose of this study was to investigate whether metabolic parameters on 18F-FDG PET/CT are associated with the Oncotype DX RS and whether 18F-FDG PET/CT can be used to predict the Oncotype DX RS.MethodsThe study group comprised 38 women with stage I/II, ER-positive/HER2-negative invasive breast cancer who underwent pretreatment 18F-FDG PET/CT and Oncotype DX testing. On PET/CT, maximum (SUVmax) and average standardized uptake values, metabolic tumor volume, and total lesion glycolysis were measured. Partial volume-corrected SUVmax (PVC-SUVmax) determined using the recovery coefficient method was also evaluated. Oncotype DX RS (0 – 100) was categorized as low (<18), intermediate (18 – 30), or high (≥31). The associations between metabolic parameters and RS were analyzed. Multivariate logistic regression was used to identify significant independent predictors of low versus intermediate-to-high RS.ResultsOf the 38 patients, 22 (58 %) had a low RS, 13 (34 %) had an intermediate RS, and 3 (8 %) had a high RS. In the analysis with 38 index tumors, PVC-SUVmax was higher in tumors in patients with intermediate-to-high RS than in those with low RS (5.68 vs. 4.06; P = 0.067, marginally significant). High PVC-SUVmax (≥4.96) was significantly associated with intermediate-to-high RS (odds ratio, OR, 10.556; P = 0.004) in univariate analysis. In multivariate analysis with clinicopathologic factors, PVC-SUVmax ≥4.96 (OR 8.459; P = 0.013) was a significant independent predictor of intermediate-to-high RS.ConclusionsHigh PVC-SUVmax on 18F-FDG PET/CT was significantly associated with an intermediate-to-high Oncotype DX RS. PVC metabolic parameters on 18F-FDG PET/CT can be used to predict the Oncotype DX RS in patients with early-stage, ER-positive/HER2-negative breast cancer.