Objective:To explore the capability of vascular endothelial growth factor receptor 2 (VEGFR2)/integrinα vβ 3 dual-targeted microbubbles in assessing the expression level of pro-angiogenic factors during renal cell carcinoma (RCC) growth. Methods:VEGFR2/integrinα vβ 3 dual-targeted microbubbles were prepared by using biotin-avidin linkage method. Twenty subcutaneous RCC xenografts in nude mice were established by subcutaneously injecting 786-O cells and then divided into 2 groups randomly. The targeted contrast-enhanced ultrasound (t-CEUS) examination was performed for all 10 mice in the first group when xenograft tumors were metered from 5 to 10 mm and >10 to 20 mm respectively. And the quantitative parameters of RCC on t-CEUS were longitudinally evaluated during tumor growth. The second group were divided into two subgroups according to xenograft tumors′ diameter, which was 5 to 10 mm and >10 to 20 mm respectively, and underwent t-CEUS examination. Quantitative analysis was performed for all t-CEUS images to obtain the targeted quantitative parameters, which including peak intensity (PI), area under the time-intensity curve (AUC), the differential tissue enhancement (dTE, presenting the difference in PI before (P 1) and after (P 2) the process of Flash). All xenograft tumors in the second group were harvested for immunohistochemical staining to observe the expression of VEGFR2, integrinα vβ 3 and CD31, and their differences in RCC with different tumor sizes. And the correlations between quantitative parameters and VEGFR2, integrinα vβ 3 and CD31 were analyzed. Results:The longitudinal comparison showed that there were statistically significant differences between AUC and dTE of RCC with different tumor sizes (all P<0.001). The larger the tumor size, the smaller the parameters were. According to the horizontal comparison, the expression levels of VEGFR2 and integrinα vβ 3 in larger RCCs were higher than those of RCCs with smaller size (both P<0.05), but there was no significant difference in CD31 expression between the two subgroups ( P=0.754). Both the targeted quantitative parameters (AUC anddTE ) and pro-angiogenic factors (VEGFR2 and integrinα vβ 3) were negatively correlated with tumor size ( rs=-0.83, -0.81, -0.70, -0.88; all P<0.05). Further more, there were good positive correlations between AUC and VEGFR2, integrinαvβ ( rs=0.76, 0.72; all P<0.05). There were good positive correlations between dTE and VEGFR2, integrinα vβ 3 ( rs=0.81, 0.70; all P<0.05). Additionally, the parameter PI was positively correlated with the expression of CD31 ( rs=0.70, P=0.025). Conclusions:The t-CEUS, mediated by VEGFR/integrinα vβ 3 dual-targeted microbubbles, allows noninvasive assessment of the expression levels of VEGFR2 and integrinα vβ 3 in RCCs, which decrease gradually with the increase of tumor size.