Background The change in apparent diffusion coefficient (ADC) measured from diffusion‐weighted imaging (DWI) has been shown to be predictive of pathologic complete response (pCR) for patients with locally invasive breast cancer undergoing neoadjuvant chemotherapy. Purpose To investigate the additive value of tumor ADC in a multicenter clinical trial setting. Study Type Retrospective analysis of multicenter prospective data. Population In all, 415 patients who enrolled in the I‐SPY 2 TRIAL from 2010 to 2014 were included. Field Strength/Sequence 1.5T or 3T MRI system using a fat‐suppressed single‐shot echo planar imaging sequence with b‐values of 0 and 800 s/mm2 for DWI, followed by a T1‐weighted sequence for dynamic contrast‐enhanced MRI (DCE‐MRI) performed at pre‐NAC (T0), after 3 weeks of NAC (T1), mid‐NAC (T2), and post‐NAC (T3). Assessment Functional tumor volume and tumor ADC were measured at each MRI exam; pCR measured at surgery was assessed as the binary outcome. Breast cancer subtype was defined by hormone receptor (HR) and human epidermal growth factor receptor 2 (HER2) status. Statistical Tests A logistic regression model was used to evaluate associations between MRI predictors with pCR. The cross‐validated area under the curve (AUC) was calculated to assess the predictive performance of the model with and without ADC. Results In all, 354 patients (128 HR+/HER2–, 60 HR+/HER2+, 34 HR–/HER2+, 132 HR–/HER2–) were included in the analysis. In the full cohort, adding ADC predictors increased the AUC from 0.76 to 0.78 at mid‐NAC and from 0.76 to 0.81 at post‐NAC. In HR/HER2 subtypes, the AUC increased from 0.52 to 0.65 at pre‐NAC for HR+/HER2–, from 0.67 to 0.73 at mid‐NAC and from 0.72 to 0.76 at post‐NAC for HR+/HER2+, from 0.71 to 0.81 at post‐NAC for triple negatives. Data Conclusion The addition of ADC to standard functional tumor volume MRI showed improvement in the prediction of treatment response in HR+ and triple‐negative breast cancer. Level of Evidence: 2 Technical Efficacy Stage: 4 J. Magn. Reson. Imaging 2019;50:1742–1753.
Background: Breast MRI has the potential to non-invasively measure response to neoadjuvant chemotherapy (NACT). We studied the effect of varying two analytic parameters used to define MRI-measured tumor volume in the prediction of pathologic complete response (pCR) to NACT and to determine if optimization of these parameter thresholds would improve the prediction of pCR. Methods: Women with locally advanced breast cancer (tumor size ≥ 3cm) were enrolled in the ACRIN 6657 / I-SPY 1 TRIAL. Each patient had up to four dynamic contrast-enhanced MRI examinations: before NACT (MR1), after one cycle of NACT (MR2), between the anthracycline-based regimen and taxane (MR3), and after NACT and prior to surgery (MR4). Breast cancer was stratified by subtypes of hormone receptor (HR), and human epidermal growth factor receptor 2 (HER2) status: HR+/HER2, HER2+, and triple negative ((TN) HR-/HER2-). MRI-measured functional tumor volume (FTV) and change in FTV (ΔFTV) were investigated as predictors of the outcome pCR. FTV is defined as the image volume with enhancement kinetics exceeding both an early percentage enhancement threshold (PEt) and a signal enhancement ratio threshold (SERt). Primary study analysis used empirically determined values. For this study PEt was varied from 30% to 200% in 10% intervals, and SERt was varied from 0.0 to 2.0 in 0.2 unit intervals. FTV was measured at each examination (FTV1, FTV2, FTV3, FTV4). ΔFTV was measured relative to the first examination (ΔFTV2, ΔFTV3, ΔFTV4). For each pair of varied PEt and SERt thresholds, the absolute and relative FTVs were re-measured and analyzed for discrimination of pCR using the area under the curve (AUC) of the receiver operating characteristic curve. Results: A total of 116 patients were included from the ACRIN 6657 / I-SPY 1 TRIAL who had complete data on all four MRI visits, HR/HER2 status, and pCR outcome. Mean age was 48 years old (range 29-69). The full cohort of 116 patients was divided into subgroups: 45 (39%) HR+/HER2-; 39 (34%) HER2+; and 30 (26%) TN. When stratified by subtypes, lower AUCs with less variation were observed in patients with HER2+ cancer than patients with HR+/HER2- and TN breast cancer. When examining prediction by visit, maximum AUCs were found at later time points in all patient cohorts. Specifically, maximum AUC was observed for the full cohort at ΔFTV3 with AUC of 0.78 (CI: 0.69–0.87) when PEt=130% and SERt=0; for HR+/HER2- subtype at ΔFTV3 with AUC of 0.9 (CI: 0.84–0.97) when PEt=130% and SERt=0 were the same as in the full cohort; for HER2+ subtype at FTV3 with AUC of 0.77 (CI: 0.62–0.92) when PEt=70%/SERt=1.4; for triple negative at FTV4 with AUC of 0.89 (CI: 0.76–1) when PEt=40%/SERt=2.0. Conclusion: This analysis suggests that the thresholds of MRI quantitative DCE measurements may need to be adjusted by breast cancer subtype to improve the predictive performance. The PEt threshold may need to be set higher in HR+/HER2- than other subtypes, which may be due to higher background parenchymal enhancement among HR+ patients. SER threshold may need to be set at higher level for triple negative subtype. A validation is underway in I-SPY 2, with a larger patient population. Citation Format: Li W, Arasu V, Jones EF, Newitt DC, Wilmes LJ, Kornak J, Esserman LJ, Hylton NM. Effect of MR imaging contrast kinetic thresholds for prediction of neoadjuvant chemotherapy response in breast cancer subtypes – Results from ACRIN 6657 / I-SPY 1 trial [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr PD3-05.
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