SMAD4 and renal cell carcinoma: Clinical prognosis analysis revealed that RCC patients with high expression of Smad1, Smad2, Smad3, Smad4, Smad9, Smad6, and TGF-βR1 had a better prognosis than did those with low expression, while RCC patients with low expression of TGF-β1 had a better prognosis than did those with high expression, and the difference was statistically significant.