Study to Evaluate Safety and Dosimetry of [18F]GEH121224 in Patients With Locally Advanced or Metastatic Breast Cancer

Group 1 : Six female patients with locally advanced or metastatic breast cancer and with HER2-positive primary tumor status will be included. These patients will receive a single injection of GEH121224 (18F) Injection and will then undergo a dynamic whole-body PET/CT scan starting at the time of injection (8 sequential scans over 90 minutes anticipated) followed by static whole-body scans starting at 120 minutes and 240 minutes after injection. Blood samples will be collected at specified time points during imaging for pharmacokinetic analysis. Safety and imaging data will be reviewed on an ongoing basis after dosing of each patient in Group 1. The injected activity may be adjusted for subsequent patients in Group 1 based on this review. A complete aggregate review of safety and imaging data will be performed by the Sponsor once all 6 patients in Group 1 have been dosed. If no safety concerns are raised, enrollment into Group 2 will start. The injected radioactivity may also be optimized before enrolling patients in Group 2. Review of safety data is described in the Safety Data Review Plan. Group 2 : Six female patients with locally advanced or metastatic breast cancer and with HER2-positive primary tumor status will be included in Group 2 and will receive a single injection of GEH121224 (18F) Injection on each of 2 separate days. On Imaging Day 1, patients will receive a single injection of GEH121224 (18F) Injection and will then undergo \[18F\]GEH121224 PET imaging at the optimal scan time identified in Group 1. Within 3 weeks (3 to 21 days; Imaging Day 2), patients will receive a second single injection of GEH121224 (18F) Injection and again undergo \[18F\]GEH121224 PET imaging at the optimal scan time identified in Group 1. Patient safety will be monitored throughout the course of the study, including a 24-hour safety follow-up by phone after each dose of \[18F\]GEH121224.