After 14 days of drug treatment, the mRNA expression level of Smad6 in RCC xenografts of mice in groups A was lower than that in groups B and C; concurrently, the mRNA expression levels of TGF-β1, TGF-βR1, Smad2, Smad3, Smad4, and Smad9 in RCC xenografts of mice in groups B and C were also reduced compared with those in group A (Figure 6). Here, SMAD6 is linked to renal cell carcinoma.