Diagnostic Potential of⁶⁸Ga-NeoB PET/CT with Estrogen Receptor– and Progesterone Receptor–Positive Breast Cancer Undergoing Staging or Restaging for Metastatic Disease

¹⁸F-FDG PET/CT has low sensitivity for estrogen receptor and progesterone receptor (ER/PR)-positive breast cancer. By contrast, gastrin-releasing peptide receptor is overexpressed in ER/PR-positive breast cancer. This study assessed the diagnostic potential of ⁶⁸Ga-NeoB PET/CT in staging or restaging metastatic ER/PR-positive and human epidermal growth factor receptor 2 (HER2)-negative breast cancer. <b>Methods:</b> Patients with ER/PR-positive and HER2-negative breast cancer with clinical suspicion for metastatic disease undergoing staging or restaging were prospectively enrolled. All patients underwent ⁶⁸Ga-NeoB PET/CT, in addition to standard ¹⁸F-FDG PET/CT. ER/PR-positive and HER2-negative status was confirmed in prior biopsy samples (primary or metastatic). Conventional imaging (¹⁸F-FDG PET/CT, bone scan, and diagnostic CT) was required within 3 wk of ⁶⁸Ga-NeoB PET/CT. ¹⁸F-FDG PET/CT and ⁶⁸Ga-NeoB PET/CT were assessed visually and quantitatively. Visually, all scans were read masked by 2 readers, with a third reader if results were discordant. <b>Results:</b> Twenty patients were enrolled, all with ER/PR-positive and HER2-negative histopathology. Of these, 75% (15/20) had lobular-subtype cancer, 40% (8/20) had suspected metastatic disease at diagnosis, and 60% (12/20) underwent restaging after systemic therapy. Overall, 75% (15/20) of the ⁶⁸Ga-NeoB PET/CT scans and 65% (13/20) of the ¹⁸F-FDG PET/CT scans were positive on visual assessment. For 50% (10/20) of patients, both scans were positive, and for 10% (2/20) of patients, both scans were negative. In the staging group, 75% (6/8) of patients had positive ⁶⁸Ga-NeoB PET/CT and 50% (4/8) of patients had positive ¹⁸F-FDG PET/CT. At restaging, 75% (9/12) of patients had positive ⁶⁸Ga-NeoB PET/CT and 75% (9/12) of patients had positive ¹⁸F-FDG PET/CT. Sites of positive ⁶⁸Ga-NeoB PET/CT and negative ¹⁸F-FDG PET/CT disease were identified in 50% (4/8) of staging patients and 42% (5/12) of restaging patients, whereas negative ⁶⁸Ga-NeoB PET/CT and positive ¹⁸F-FDG PET/CT disease was found in none of the staging patients but 58% (7/12) of the restaging cohort. Of these, 71% (5/7) of patients had a reduction in their ER status in the most recent biopsy samples. Quantitatively, the median SUV_max was higher for ⁶⁸Ga-NeoB PET/CT (20.5; interquartile range, 5.8-31.3) than for ¹⁸F-FDG PET/CT (7.4; interquartile range, 4.9-9.8). <b>Conclusion:</b> ⁶⁸Ga-NeoB PET/CT has diagnostic potential in the staging of ER/PR-positive and HER2-negative breast cancer. Further evaluation is warranted.