472 Utility of [89Zr]Trastuzumab-PET/MRI Imaging for Quantitative Assessment of Tumor Heterogeneity In HER2+ Breast Cancer

OBJECTIVES/GOALS: This study was performed to explore the capabilities of simultaneous [89 Zr]trastuzumab-PET/MRI acquisition in a cohort of metastatic HER2+ breast cancer. The insights derived provide additional noninvasive characterization and precise intratumoral analysis tools for healthcare providers. METHODS/STUDY POPULATION: A total of 13 patients, aged between 40 and 70, diagnosed with HER2-positive breast cancer, were selected to participate in this study. Whole-body [89 Zr]trastuzumab-PET/MR imaging was performed 5 ± 1 days post-injection of the radiopharmaceutical during ongoing HER2-directed therapy. Concurrently acquired T1-weighted MRI facilitated the identification of normal organ and tumor regions of interest, which were further analyzed for mean ADC and mean standardized uptake value. Multiparametric intratumoral habitat analysis was performed. Utilizing the median metric values, tumors were evaluated for heterogeneity, specifically assessing high and low HER2 expression through an image processing framework in conjunction with ADC metrics. Long-term treatment response evaluation is ongoing. RESULTS/ANTICIPATED RESULTS: Initial analysis indicate all tumors exhibited higher overall uptake of [89 Zr]trastuzumab across various sites including the bone (p=0.019), brain (p=0.014), and breast (p=0.069), when compared to corresponding normal organs. Additionally, increased ADCmean values were observed in all regions besides brain tumors (bone: p=0.002, brain: p=0.5, breast: p=0.03, juxtapulmonary: p=0.037), indicating distinct patterns of cellularity. Notably, one of five patients with a breast lesion, who exhibited a complete response to HER2-targeted therapy, exhibited the highest breast lesion SUVmean. Brain and lymph node lesions demonstrated intratumoral heterogeneity of HER2 expression. Qualification of multi parametric maps is anticipated to inform on intratumoral heterogeneity DISCUSSION/SIGNIFICANCE: Despite limitation in clinical applications of quantitative approaches due to lack of standardization of processing, initial investigations, in combining molecular imaging of HER2 and quantitative MRI demonstrate potential in characterizing metastatic HER2+ breast cancer for intratumoral classification and therapeutic stratification.