Monitoring Breast Tumor Lung Metastasis by U-SPECT-II/CT with an Integrin αvβ3-Targeted Radiotracer 99mTc-3P-RGD2

PURPOSE The purpose of this study was to evaluate the capability of u-SPECT-II/CT to monitor the progression of breast cancer lung metastasis using (99m)Tc-3P-RGD(2) as a radiotracer. METHODS The breast cancer lung metastasis model was established by tail-vein injection of 2 x 10(5) - 1.5 x 10(6) MDA-MB-231 cells into each athymic nude mouse. SPECT/CT studies were performed at a specified time after inoculation of MDA-MB-231 cells. Histological staining was used to further confirm the presence of lung metastases. RESULTS We found that both inoculation time and tumor cell load had significant influence on the extent of lung metastasis. For example, if animals were injected with 2 x 10(5) MDA-MB-231 cells, there were no detectable metastatic breast tumors in the lungs after 8 weeks. If animals were injected with 1 x 10(6) MDA-MB-231 cells, there were many tumors in both lungs at week 8. When 1.5 x 10(6) MDA-MB-231 cells were injected, the animal became very weak by week 7. We also found a rare example of breast cancer metastasis in the muscle and mediastinal lymph nodes. The tumor necrotic regions were clearly delineated by u-SPECT-II/CT. CONCLUSION This study clearly demonstrated that (99m)Tc-3P-RGD(2) is an excellent radiotracer for noninvasive imaging of metastatic breast tumors in the lungs, mediastinal lymph nodes and muscles. (99m)Tc-3P-RGD(2) SPECT/CT is an outstanding platform for monitoring the progression of breast cancer lung metastases, semi-quantification of breast tumor load in the lungs and delineation of tumor necrosis in small animals.