A Study of the Biological Characteristics of Breast Cancer by Using Tc-99m MIBI Scintigraphy

ABSTRACT

BACKGROUND: Some researchers have tried to use Tc-99m MIBI (2-methoxyisobutyl isonitril) scintigraphy to evaluate breast-cancer patients. Early reports revealed that Tc-99m MIBI breast scintigraphy was useful in distinguishing malignancies from benign masses in patients for whom mammographic evaluations were difficult. Further studies suggested that functional imaging with Tc-99m MIBI in breast cancer seemed to be correlated with the levels of P-glycoprotein (Pgp) expression and angiogenesis in cancer tissues. For that reason, we evaluated whether significant relationship actually existed between the pattern of Tc-99m MIBI uptake in tumor tissue and tumoric factors including Pgp expression and angiogenesis. METHODS: Thirty-one untreated breast-cancer patients (later pathologically proved to have had invasive ductal carcinomas) were prospectively studied by using both Tc-99m MIBI scintigraphy on and immunohistochemical analyses of angiogenesis and Pgp expression in sugically removed tumor tissues. Both lateral and anterior planar images were obtained at 10 minutes and 3 hours after intravenous injection of 740 MBq Tc-99m MIBI. The tumor-to-normal breast ratio (T/N) and the washout index (WI, early T/N minus late T/N divided by early T/N) were calculated. RESULTS: A significant correlation was found between the T/N's at early and late images (r=0.54, p=0.002 on early images; r=0.47, p=0.006 on late images). The T/N's of early images were not different among the different groups of Pgp expression (p=0.3696) while those of late images were significantly different among the groups (p=0.0276). An even more significant difference was noted in the WI's among the groups (p=0.0015). A significant negative correlation was noted between the T/N of late images and Pgp expression (p=0.0276). An even stronger correlation was found between WI and Pgp expression (r=0.668, p=0.001). CONCLUSIONS: The tumoral uptake and washout of Tc-99m MIBI can be used as a simple functional test for angiogenesis and P-glycoprotein expression in untreated breast cancer.