Abstract PO2-06-13: Promising clinical performance of 89Zirconium-labelled Girentuximab PET-CT for imaging metastatic triple negative breast cancer patients (OPALESCENCE)

Abstract Aim: Triple Negative Breast Cancer (TNBC) is aggressive, often with a metastatic evolution and drug-resistant with limited therapeutic options. Evaluating new markers is an unmet need. Recently, the combination of anti-angiogenic and targeted hypoxia effectors agents proved to enhance therapy response. Indeed, anhydrase Carbonic-IX (CA-IX), a hypoxia-mediated breast tumor growth regulator, is important for the BC stem cells maintenance within hypoxic region and is highly overexpressed in TNBC. This pilot prospective study “OPALESCENCE” (NCT04758780) aimed at assessing PET/CT with 89Zr-labeled girentuximab (89Zr-TLX250) targeting CA-IX in 12 metastatic TNBC patients. Methods: Patients underwent FDG and 89Zr-TLX250 PET-CT and conventional imaging (CI) if needed (CT, US, mammography, brain MRI). Without any premedication or dietary preparation, patients received a single slow intravenous administration of 37±10% MBq 89Zr-TLX250 (10 mg). Day 3 or 5 post injection, a skull to mid-thigh PET/CT was acquired with 10 minutes acquisition time per bed position. The gold standard was determined by FDG PET/CT, CI and follow-up; lesion detected at least by 2 modalities was considered as true positive. Immunohistochemistry (IHC) was performed with Bond RX fully automated research stainer with CA-IX antibody (Leica, clone TH22). Staining was evaluated with semi-quantitative analysis (percentage and intensity of tumor cells expression). Human anti-chimeric antibody (HACA) were sampled but will be determined at study end. Results: Enrolment has been completed, a total of 273 lesions confirmed by gold standard as shown on table 1 were detected in 12 patients (231 by 89Zr-TLX250 and 264 by FDG PET/CT). Overall sensitivity of 89Zr-TLX250 PET/CT was 87.5%, with 100% sensitivity for breast, skin, adrenal gland and brain and 88.0%, 91.9% for nodes and bone respectively. Overall sensitivity for FDG-PET/CT was 96.7%. According to table 2, 6 patients had 100% of their lesions highlighted by 89Zr-TLX250 PET. In addition, for 2 other patients only one of the lesions was not detected by immunoPET. 89Zr-TLX250 PET therefore detected almost all of the metastatic lesions in 67% of the patients. For 8/12 patients, IHC was analysed and for 6 patients, CA-IX expression lesions was from 100% to 10% with an intensity from 3+ to 2+, whereas two patients presented no Ca-IX expression on tumour lesions. No 89Zr-TLX250 safety issue was reported. Conclusion: 89Zr-TLX250 PET/CT seems very promising because it allows the CA IX status lesions knowledge on whole body scale with a minimally invasive way, unlike the information provided by biopsies corresponding to only 1 or 2 lesions studied. Moreover, these results illustrated interest of 89Zr-TLX250 PET/CT as targeting agent for TNBC patients leading above all to a theranostic approach possibility. Study analysis (specially IHC, HACA and semi-quantitative PET/CT analysis) is ongoing and supplementary data will be presented during the congress. This is an investigator initiated trial. Investigational medicinal product was provided by Telix Pharmaceuticals. Table 1: Sensitivity of 89Zr-TLX250 PET, FDG PET, and conventional imaging (US, brain MRI and Mammography). Table 2: Number of confirmed lesions according to Gold Standard detected by 89Zr-TLX250 PET/CT (iPET), FDG PET/CT and CI for each patients. Citation Format: Caroline Rousseau, Marie Francoise Heymann, Jean Sebastien FRENEL, Elise Picot-Dilly, Maelle Le Thiec, Manon Taupin, Alexis Mouton, Emmanuelle Bourbouloux, Agnès Morel, Nadia Allam, Amélie Mallet, Mario Campone, Ludovic Ferrer, Françoise Kraeber-Bodéré. Promising clinical performance of 89Zirconium-labelled Girentuximab PET-CT for imaging metastatic triple negative breast cancer patients (OPALESCENCE) [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 PO2-06-13.