CA9 and renal cell carcinoma: Although the idea of using CA9 and CD147 to attract CTCs is new, the characteristics of these molecules along with their high expression in RCC suggest their potential use as RCC CTC-capture antigens [53, 58, 59], which is supported by our findings that the combined use of CA9 and CD147 as capture antigens retrieved CTCs from both CTC-mimicking renal cancer cells as well as RCC patient blood with significantly improved capture efficiency compared to the EpCAM-based capture method (Figure 3).