We analyzed the relationship between level of let-7d and the mRNA levels of COL3A1 and CCL7 in clinical RCC tissues by quantitative real-time RT-PCR Significant inverse correlation was found between let-7d level and COL3A1 mRNA level in the 80 clinical RCC samples (Figures 6K and 6 L), and between let-7d level and CCL7 mRNA level in the clinical RCC samples with T3 stage. Here, COL3A1 is linked to renal cell carcinoma.