Abstract P4-12-12: Quantitative in vivo imaging of intratumoral heterogeneity to assess tumor response to trastuzumab treatment in a preclinical model of HER2+ breast cancer
Authors: Syed A , Quarles CC , McIntyre JO , Barnes SL , Yankeelov TE , Sorace AG 
Published: March 2017

Abstract
Introduction:
Intratumoral heterogeneity is associated with variable treatment response and poorer patient prognosis. Initial changes in intratumoral cellular and vascular heterogeneity after treatment could serve as an early metric for treatment response and be used to guide and optimize therapy for improved patient outcome. Quantitative, noninvasive imaging can characterize, in 3D, tumor response to treatment by evaluating longitudinal alterations in heterogeneity. Our goal is to quantitatively image the changes in intratumoral cellular and vascular heterogeneity in response to trastuzumab in a murine model of HER2+ breast cancer.
Experimental Design:
Data from two independent cohorts of mice were used in this study. Mice were implanted subcutaneously with BT474 breast cancer cells (1×107) and randomly assigned to trastuzumab treated (10 mg/kg) or saline control groups. After tumors reached ~225 mm3, intraperitoneal injections of trastuzumab or saline were given on days 0 and 3. In the first cohort of mice (n=14), quantitative dynamic contrast enhancement magnetic resonance imaging (DCE-MRI) assessed tumor response on days 0 (prior to treatment), 1 and 4. In this study, we focused on the calculated extravascular extracellular space, measured using DCE-MRI parameter, ve. In the second cohort of mice (n=10), 18F-flouromisonidazole positron emission tomography (FMISO-PET) imaging was utilized to assess tumor hypoxia on days 0 (prior to treatment), 1, 3, 4, and 7 through changes in standardized uptake value (SUV). Longitudinal changes in heterogeneity were assessed using voxel based histogram analysis of ve or SUV. Statistical analysis (R Studio) compared histogram analyses (full-width half-maximum, range, kurtosis, and standard deviation) of control and treated groups. Tumor size measurements obtained at the conclusion of the experiment were used to validate imaging findings of tumor response to treatment.
Results:
DCE-MRI revealed increased heterogeneity in extravascular extracellular space after trastuzumab treatment, as quantified by a significant increase in the FWHM of ve voxel distributions at day 4 post-treatment (p=0.03). Additionally, the FMISO-PET data showed a significant decrease in hypoxic regional heterogeneity in treated tumors, as quantified by percent change (normalized to baseline) in standard deviation and range of SUV tumor voxel distributions on days 3 (p=0.02), 4 (p=0.01), and 7 (p&lt;0.001) compared to saline controls.
Conclusion:
Trastuzumab improved oxygen delivery throughout the tumor as quantified by decreased hypoxia heterogeneity (narrowing of distributions) of the FMISO-PET SUV map. Likewise, the increased heterogeneity (widening of distributions) of the DCE-MRI ve parametric map, reflects a more heterogeneous cellularity interpreted to arise from enhanced cell death following trastuzumab treatment. Ongoing analysis of heterogeneity of corresponding histology slides will be used to validate the imaging measures of heterogeneity. DCE-MRI and FMISO-PET reveal quantitative longitudinal changes in tumor cellular and vascular heterogeneity, and may be able to predict response and guide therapy for patients with HER2+ breast cancer.
Citation Format: Syed A, Quarles CC, McIntyre JO, Barnes SL, Yankeelov TE, Sorace AG. Quantitative in vivo imaging of intratumoral heterogeneity to assess tumor response to trastuzumab treatment in a preclinical model of HER2+ breast cancer [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 P4-12-12.