Abstract P6-10-17: Breast MRI as a radiomic biomarker of immune response in HER2+ breast cancer

Abstract

Abstract Rationale/Objectives: Tumor immune infiltration in HER2+ breast cancer is associated with improved outcomes and better responses to treatment with drugs such as trastuzumab. Breast MRI is a non-invasive technique that is part of the standard evaluation for localized breast cancer. Breast MRI dynamic-contrast enhanced (DCE) and diffusion-weighted imaging (DWI) sequences may detect immune responses in the tumor microenvironment. Apparent diffusion coefficient (ADC), which is derived from DWI, has been associated with tumor cellularity. In this pilot study, we hypothesized that patients with low ADC would be more immune responsive (i.e. have greater TIL infiltration) to trastuzumab. We also performed an exploratory analysis looking at differences in the expression of immune-relevant genes between “low” and “high” ADC patients. Methods: Patients with localized HER2+ breast cancers 10 mm or larger and planned for curative-intent therapy were eligible to enroll. After enrollment, patients received a single run-in dose of trastuzumab with paired breast MRI exams before and after treatment that included DCE and DWI sequences. Post-trastuzumab tissue was obtained from the patient’s surgical specimen or from a second biopsy (if planned for additional neoadjuvant treatment). MRI images were analyzed to measure the functional tumor volume and peak signal enhancement ratio from DCE and mean apparent diffusion coefficient (ADC) from DWI. TIL content was assessed by a breast pathologist in both the pre- and post-trastuzumab tissue specimens. The pre- and post-treatment samples were also analyzed using an immune-focused RNA-based multiplex gene expression assay. Results: Twelve women have enrolled to date with a median age of 53 years (range 37-70 years old). Five out of the twelve patients (42%) had estrogen-receptor negative tumors. For the 8 patients with pre- and post-treatment tissue currently available for analysis, the average pre-treatment TIL percentage was 22% (range 1-70%), the average post-treatment TIL percentage was 42% (range 1-90%), and the average absolute increase between pre- and post-treatment TILs was 20% (range 0%-58%). Pre- and post-treatment ADC showed a strong negative correlation with the increase in TIL content after trastuzumab treatment (r = -0.71 and r = -0.93, respectively). At submission, preliminary gene expression analysis of pre- and post-treatment tissue is available in 6 patients. The patients were binned into “high” and “low” ADC groups with the median pre-treatment ADC as the cut-off. The magnitude of change in gene expression after trastuzumab treatment (small vs large change) clustered by high or low pre-treatment ADC; this suggests that pre-treatment ADC may differentiate between two distinct immune phenotypes. Further analysis showed that the low ADC group had relatively higher pre-treatment gene expression of CD8, CD4, and CD19 (T and B cell markers) when compared to the high ADC group. The low ADC group also had a decrease in FoxP3 expression (regulatory T cell marker) versus the high ADC group, which had an increase in FoxP3 expression. The high ADC group also had a notable increase in CCR4 expression (associated with a TH2 type immune response), while the low ADC group did not have an increase. The combination of an increase in FoxP3 expression and an increase in CCR4 expression suggests that the high ADC group may have a more immune-inhibited microenvironment in response to trastuzumab. Conclusions: These initial analyses suggest that the pre-treatment ADC calculated from DWI may identify HER2+ breast cancers that will have an anti-tumor immune response to trastuzumab therapy. Final data from the full planned cohort will be presented at the meeting and include discussion of the DCE metrics. Based on this preliminary data, further study of breast MRI as an immune biomarker is warranted. Citation Format: Laura Carpin Kennedy, Grace Durenberger, Sasha E. Stanton, Shaveta Vinayak, Suzanne Dintzis, Savannah Partridge, VK Gadi. Breast MRI as a radiomic biomarker of immune response in HER2+ breast cancer [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P6-10-17.