Monitoring Breast Tumor Lung Metastasis by U-SPECT-II/CT with an Integrin α(v)β(3)-Targeted Radiotracer( 99m)Tc-3P-RGD(2)

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.