Abstract Background: Microwave imaging has been proposed as an alternative method of breast imaging that is low-cost and comfortable for women as it avoids compression. Microwave properties of tissues relate to water content and behaviour (Gabriel et al, 1996); specifically, low water content tissues (e.g. fat) have lower properties, while higher water content tissues (e.g. gland) have greater properties (Lazebnik et al, 2007). Diseased tissues with higher water content, such as cancer, exhibit increased microwave properties (e.g Sujitani et al, 2015). These differences in microwave signatures of healthy and diseased tissues provide the opportunity to detect tumors and monitor treatment progress. Previously, we have reported detection of tumors with a microwave imaging system in 15 patients (Mojabi et al, 2025a) and presented case-studies of 6 participants undergoing neoadjuvant chemotherapy (Mojabi et al, 2025b, conditionally accepted). Purpose: We explore the feasibility of tracking treatment-related changes in the breast with microwave imaging in a pilot study with women undergoing neoadjuvant chemotherapy for breast cancer. Methods: The prototype microwave imaging system consists of two plates which are placed in contact with the breast (Mojabi et al, 2024). Microwave transmitters and receivers are embedded in the plates; signals transmitted through the breast are used to estimate microwave frequency properties of tissues, and maps of these estimates form a 2D image. Images are collected in both craniocaudal (CC) and mediolateral oblique (MLO) views to facilitate comparison with mammography. 16 participants were recruited and provided written informed consent. Participants had pathologically confirmed diagnosis of early-stage or locally advanced breast cancer and received upfront neoadjuvant chemotherapy based on guidelines. Participants received standard of care treatment for 6-8 cycles and were scanned with the microwave imaging system prior to each treatment cycle. Participants also underwent mid-point imaging (primarily ultrasound), and relevant clinical data was obtained. Results: The images of the non-cancerous breast serve as an intra-patient reference; comparison of the bilateral images may be used to identify the presence of the tumor at baseline pre-treatment. In one group of patients (9/16), a single tumor was present in a location expected to be captured by the scanner. In these cases, increased average properties and/or localized responses suggest detection of the tumor in at least one view at baseline. Potential for tracking changes was suggested by trends in average properties for 7 patients; trends were less evident with changes in separation between the plates at serial scans and smaller breast sizes. The second group of patients (7/16) had multifocal tumors or other clinical factors that likely impacted the scans. One patient had breast implants, while separations between scanner plates for another were up to 4 cm greater for the breast with the tumor, resulting in poor images. Two patients had tumors in locations that were likely not positioned in the scanner. Of the 3 patients with multifocal tumours, detection was noted at baseline in two cases and potential to track changes in one case. Conclusions: Breast microwave imaging shows promise as an imaging biomarker of treatment response in patients receiving upfront neoadjuvant systemic therapy, when used serially. Scans of the cancerous and contralateral non-cancerous breast serve as an intra-patient control. Ongoing analysis is aimed at improving imaging algorithms to support automated detection of tumors. Further evaluation with a larger cohort of subjects is warranted. Citation Format: P. Mojabi, R. Tsang, J. Bourqui, A. Garland, Z. Lasemiimeni, D. Deutscher, B. Docktor, E. Fear. A new imaging approach for monitoring neoadjuvant chemotherapy abstract. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS1-06-25.
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