CCL7 and renal cell carcinoma: To further assess whether let-7d is involved in the proliferation, migration, and tumor macrophage infiltration of RCC by targeting COL3A1 and CCL7, we inhibited the expression of let-7d with a synthesized let-7d inhibitor in a relatively low metastatic OS-RC-2 cell line with high endogenous let-7d expression level (Figure 6A).