99mTc-HPArk2 SPECT/CT in the evaluation of HER2-positive breast cancer: a pilot prospective study

556 Purpose: This prospective pilot study investigated the use of 99mTc-HPArk2, an antagonist targeting human epidermal growth factor receptor 2 (HER2), for evaluating breast cancer using SPECT/CT. Methods: With institutional review board approval and informed consent, 20 female patients suspected of breast cancer based on mammography or ultrasonography were recruited. Within 1 week before surgery, the patients underwent SPECT/CT scans at 30 minutes after intravenous injection of approximately 11.1MBq (0.3mCi) per kilogram body weight of 99mTc-HPArk2 and 18F-FDG PET/CT scans 60 minutes after intravenous injection of approximately 5.6MBq (0.15mCi) per kilogram body weight. So far, 15 patients were pathologically diagnosed as breast cancer. Among them, 6 patients had ipsilateral lymph node metastasis. Standardized uptake values (SUV) were obtained by a self-made software and referring to phantom study. Results: No radiopharmaceutical-related adverse event was observed in the patients. 99mTc-HPArk2 SPECT/CT detected the primary tumor well in 14/15 (93%) patients, and the lymph node metastasis in 5/6 (83%) of the patients, whereas the other 1 patient demonstrated only micro-metastasis in lymph nodes. The SUVmax were1.60±0.87 in the breast cancer, and 0.94±0.42 in the lymph node metastasis. The SUVmax of HER2(3+) tumors (2.45±1.19) were significantly higher than those in HER2(-) or HER2(1+) tumors(0.916±0.37, P=0.006).The normal breast tissue (NBT) showed low to moderate 99mTc-HPArk2 binding, with a SUVmax of 0.78±0.31 and a SUVmean of 0.70±0.26. The intensity of 99mTc-HPArk2 uptake in the breast cancer was significantly associated with HER2 immunohistochemistry results. There was a significant positive correlation between the SUVmax of 99mTc-HPArk2 and the HER2 expression level (r = 0.863, P = 0.001). Conclusions: This pilot study indicated that the uptake of HER2 antagonist 99mTc-HPArk2 correlate with HER2 expression in breast cancer. 99mTc-HPArk2 SPECT/CT can provide specific, non-invasive evaluation of HER2 expression in breast cancer.