Abstract PO5-26-02: Changes in Breast Cancer Optoacoustic Imaging Features During Neoadjuvant Therapy and Correlation with Pathologic Response: A feasibility study
Authors: Dogan Baṣak , Ozcan Berat Bersu , McArthur Heather , Peng Yan 
Published: May 2024

Abstract
Purpose: To evaluate the association of optoacoustic imaging (OA/US) feature changes with neoadjuvant therapy response and compare with volumetric changes.
Methods and Materials: In an IRB approved, HIPAA compliant single arm, single-institution study, 20 breast cancer patients scheduled to undergo neoadjuvant systemic chemotherapy (NAC) were prospectively enrolled to undergo optoacoustic imaging (OA/US) at baseline, prior to cycle 2(Postcycle 1), mid-therapy (mid-chemo)and pre-operative(pre-op) timepoints using a standardized scan protocol. % change in volume was recorded for each timepoint. OA/US features: internal vessels (OAint), total internal hemoglobin (OAHb), internal deoxyHb, external peripheral zone (OApz), boundary zone (OAbz) scored using a previously validated schema. Pathology was collected from standardized reports using residual cancer burden (RCB) and pathologic complete response (pCR) as end points. RCB0-II were classified as responders, RCB-III as non-responders. Descriptive statistics displayed as mean and standard deviation and compared using Wilcoxon Rank-Sum test. Association of volume change was performed using odds ratio (OR) generated from univariate logistic regressions (P-Value &lt; 0.05 for significance).
Results: Mean patient age was 50.4 years (SD± 9.5), index cancer size: 26.3mm (SD±9.7). Surgical pathology showed pCR in 6(30%), partial response in 11(55%), no response in 3(15%) cancers, with mean overall residual cellularity of 32.7%(SD±33.5). Mean % residual volume was not significantly different between responders vs nonresponders. [PostCycle 1 (43.7 ± 25.3 vs 38.5 ± 24.8, p=0.7), mid-chemo (64.2 ± 30.9 vs. 65.8 ± 24.6, p=0.8), pre-op (82.9 ± 23.5 vs 89.3 ± 8.4, p=0.9) timepoints. Regression analysis did not show significant correlation of %vol change with pCR at any timepoint (p &gt;0.05). Postcycle 1, OAHb change was significantly higher in patients who had pCR (76.4% vs 108.8%; p=0.02). At pre-op scan, greater decreases were seen in all OA/US scores in cancers that achieved pCR compared to non-pCR [OAbz (25.0% vs. 84.7% P = 0.03; OAint (40.0% vs. 90.3% P = 0.03);OAHb (18.3% vs. 91.8%; P = 0.03); deoxyHb (26.7% vs. 104.8%; P = 0.02), total OAext (25.8% vs. 88.1%; P = 0.03); total internal (16.2% vs. 91.6%; P = 0.03)].
Conclusions: OA/US feature changes demonstrate higher correlation with pCR than volumetric shrinkage in this feasibility study and show promise as a potential tool to non-invasively identify pCR.
Table. Percentage Change in Optoacoustic Ultrasound (OA/US) Feature Scores from Baseline, Stratified by (pathologic complete response (pCR).
Citation Format: Baṣak Dogan, Berat Bersu Ozcan, Heather McArthur, Yan Peng. Changes in Breast Cancer Optoacoustic Imaging Features During Neoadjuvant Therapy and Correlation with Pathologic Response: A feasibility study [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-26-02.