The mean concentration of mutant DNA in the bile ctDNA from BTC patients (14,995 copies/mL) was about 10-fold higher than that of the control patient with a CBD stone (1000 copies/mL; Figure 3A), and we set the cut-off value for KRAS mutations at >1500 copies/mL (Table 2). Here, KRAS is linked to red-green color blindness.