Abstract
242084
Introduction: PET imaging and radionuclide therapy using the gastrin-releasing peptide receptor (GRPR) antagonist NeoB can offer new theranostic options for patients with various solid tumors. 68Ga-NeoB PET can be used to identify candidates with sufficient tumor uptake for 177Lu-NeoB radionuclide therapy. Here, we use 68Ga-NeoB PET to evaluate tumor uptake in patients with breast cancer.
Methods: Patients were enrolled in a prospective observational trial. PET imaging was performed after a mean of 85 min (range: 48-153) after injection of 90 MBq (33-145) of 68Ga-NeoB. 68Ga-NeoB uptake was analyzed in five anatomical categories that were derived from TNM classification (breast, lymph nodes, liver, bone, other). In any region that was NeoB-positive (defined as a region that exhibits higher uptake than local background), SUVmax and peak tumor-to-liver ratio (TLRpeak) of the hottest lesion were determined. Mean SUVmax and TLRpeak were calculated as mean of all NeoB-positive regions per patient and defined as global mean SUVmax and TLRpeak.
Results: We enrolled 29 patients with breast cancer (23 ER+/HER2-, 3 ER+ or -/HER2+, 3 triple-negative; 12 with distant metastases) in this study who received a total of 36 68Ga-NeoB PET scans. We excluded 7 scans that were re-staging scans in the same individuals and scans of 3 patients that did not exhibit metabolically active tumor. 10 of these remaining 26 patients had newly diagnosed and 16 had persistent/recurrent breast cancer. 18/20 ER+/HER2- patients (90.0%), 2/3 ER+ or -/HER2+ (66.7%), and N=0/3 triple-negative patients were NeoB-positive in any region. Therefore, we focused our analysis on ER+/HER2- patients: The mean (range) global mean SUVmax and TLRpeak values were 9.6 (4.1-25.9) and 2.6 (0.6-8.6), respectively. Grouping these patients according to their mean SUVmax values showed 2/18 (11.1%) patients with very high global NeoB uptake (SUVmax≥20), 5/18 (27.8%) patients with high global NeoB uptake (SUVmax≥10), 6/18 patiens (33.3%) with intermediate global NeoB uptake (10>SUVmax≥5), and 5/18 (27.8%) with low global (5>SUVmax) NeoB uptake. In a region-based analysis in ER+/HER2- patients, 77.8% (28/36) of regions with metabolically active tumor were NeoB-positive. In these regions, mean (range) SUVmax and TLRpeak were 11.3 (1.7-44.0) and 3.4 (range: 0.4-14.9), respectively. Lymph node and distant metastases showed a trend towards higher SUVmax and TLRpeak values than local tumor. Global mean SUVmax and TLRpeak did not show a significant correlation to the level of ER expression (p=0.23/0.54).
Conclusions: Patients with ER+/HER2- breast cancer showed the highest rate of NeoB-positive disease. In these patients, global uptake was larger than liver uptake in about 2/3 of patients with 1/3 of patients showing global high or very high uptake. Future evaluations are warranted to identify candidates for 177Lu-NeoB radionuclide therapy in a theranostic approach.