NPTX2 and renal cell carcinoma: However, the limitations of this study were: 1) not further determining the clinical diagnostic and prognostic values of circ_0054537 in RCC, 2) not further probing into the precise mechanism of circ_0054537-miR-640-NPTX2 axis displaying these cellular functions, and 3) not further testing the role of circ_0054537 knockdown in tumor metastasis in nude mice.