Abstract PS4-04-10: Preclinical Evaluation of 64Cu-Labeled Cetuximab Immuno-PET for Detecting Sentinel Lymph Node Metastasis and Assessing Therapeutic Potential in EGFR-Positive Breast Cancer

Abstract Background: Accurate detection of sentinel lymph node (SLN) metastasis remains a diagnostic challenge in breast cancer. This study aimed to evaluate the feasibility of immuno-positron emission tomography (PET) using 64Cu-labeled cetuximab for detecting SLN metastasis and to assess its preliminary therapeutic effect in a preclinical model of epidermal growth factor receptor (EGFR)-positive breast cancer. Methods: The SLN metastasis model was established using EGFR-overexpressing MDA-MB-468 breast cancer cell line. [64Cu]Cu-PCTA-cetuximab was administered either intravenously (IV; 5.8 ± 0.9 MBq; n=12) or intradermally / subdermally (ID/SD; 4.3 ± 0.4 MBq; n=11) into the parapapillary region of the tumor-containing mammary gland. PET/computed tomography scans were performed 24 h after tracer injection, with delayed imaging at 48 h to evaluate retention and contrast. For comparison, 18F-FDG PET was also performed via IV (9.1 ± 1.4 MBq, n = 4) or ID/SD (5.4 ± 2.2 MBq, n = 3) routes in the same cohort. SLNs were identified using blue dye, and were pathologicaly evaluated for metastases. To evaluate therapeutic efficacy, additional mice received IV [64Cu]Cu-PCTA-cetuximab at 9, 18, or 37 MBq (n = 3 per group), and tumor diameters and body weight were monitored over time in comparison to untreated controls. Results: After intravenous administration of [64Cu]Cu-PCTA-cetuximab (n=12), radiotracer accumulation was detected in the primary tumor in all mice and in the axilla of eight mice (67%, SUVmax 1.24 ± 0.51), all of which were found to have SLNs with histologically confirmed metastasis. The sensitivity, specificity, accuracy, and negative and positive predictive values for PET imaging in this group were 89%, 100%, 92%, 75%, and 100%, respectively. In the ID/SD group , all 11 mice showed high tracer accumulation in both the primary tumor and axillary nodes (SUVmax 4.28 ± 1.19); however, only six mice (55%, SUVmax 5.01 ± 1.12) had histologically confirmed SLN metastasis. The sensitivity, specificity, accuracy, and positive predictive values for this route were 100%, 0%, 55% and 55%, respectively. SLN metastasis was not detectable by 18F-FDG PET regardless of the administration route. Regarding therapeutic evaluation, all IV-treated groups showed tumor growth suppression compared to controls. The 37 MBq group exhibited the most pronounced tumor reduction but also showed a marked decrease in body weight, indicating potential systemic toxicity at higher doses. Conclusions: Immuno-PET with IV-administered [64Cu]Cu-PCTA-cetuximab demonstrated high precision for diagnosis of SLN metastasis and showed promising therapeutic efficacy in an EGFR-positive breast cancer model. While ID/SD administration showed lower diagnostic specificity, its strong accumulation in SLNs indicates potential utility for localized therapy. These findings support further exploration of 64Cu-labeled cetuximab for theranostic applications in breast cancer. Citation Format: T. Usui, T. Miyake, T. Watabe, K. Hiroki, K. Abe, T. Ryu, S. Yasufumi, N. Masunaga, C. Mishima, M. Tsukabe, Y. Sota, T. Yoshinami, T. Tanei, K. Shimazu. Preclinical Evaluation of 64Cu-Labeled Cetuximab Immuno-PET for Detecting Sentinel Lymph Node Metastasis and Assessing Therapeutic Potential in EGFR-Positive Breast Cancer [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 PS4-04-10.