Preliminary assessment of the diagnostic value of 64Cu-SAR-Bombesin PET-CT imaging for staging of ER+/PR+HER2- metastatic breast cancer disease: comparison with conventional imaging.

1107 Introduction: Prognosis of metastatic breast cancer remains poor with an overall five-year survival of 26%, hence, accurate staging and new therapy options are paramount. 18F-Fluorodeoxyglucose (FDG) PET-CT is highly sensitive in patients with triple negative breast cancer. However, the majority of breast cancers are oestrogen receptor (ER) and progesterone receptor (PR) positive, human epidermal growth factor 2 negative (HER2-), for which FDG PET-CT scans has significantly lower sensitivity. It is has been shown that ER+/PR+ status is strongly associated with gastrin releasing peptide receptor (GRPR) expression. 64Cu is an alternate PET radioisotope with theranostic potential (67Cu), which is stably chelated using the sarcophagine (SAR) chelator. The aim of this study is to evaluate the potential of 64Cu-labelled receptor antagonist, 64Cu-SAR-Bombesin, for PET-CT in the staging of recurrent metastatic ER+/PR+/HER2- breast cancer. Methods: This phase 1 study is prospectively enrolling 10 patients with clinical progression of biopsy proven metastatic ER+/PR+/HER2- breast cancer. 200 MBq of 64Cu Sartate Bombesin (SAR BBN) is injected intravenously with imaging at 1, 3 and 24 hours post-injection; biochemical, haematological and coagulation serum levels, vital signs and electrocardiogram (ECG) are monitored. Blood clearance is assessed by measuring activity concentration in blood samples taken at the same time points as imaging. Staging is assessed by conventional imaging (FDG, bone scan and diagnostic CT) within 3 weeks of SAR BBN imaging. Scans are analysed both visually, and with total lesional quantitation including total tumour burden, SUV max, SUV mean and total lesions (MIM Software, Cleveland). Receptor status of tissue from biopsy at the time of diagnosis, as well as tissue from additional metastatic site biopsies are collected from histopathology reports. Results: To date, 4/10 patients have been enrolled and undergone trial imaging. The remaining 6/10 patients will be recruited in the next 4 months. The study will assess safety of SAR BBN injection in addition to blood clearance, serial lesional washout and optimal timing of imaging post injection. Comparison of total lesional quantitation measures between SAR BBN and FDG PET CT will also be undertaken. Conclusions: This phase 1 in vivo study will provide information to determine the safety profile and optimal time of injection of SAR BBN, in addition, to preliminary information on diagnostic accuracy of SAR BBN compared to FDG and conventional imaging in ER+/PR+ breast cancer.