The sample was partitioned into 20,000 droplets by using droplet digital PCR (ddPCR) (QX200; Bio-Rad, Hercules, CA) (20 (link),21 (link)). The DNA was concentrated and distributed among these droplets randomly. The authors tested for 3 types of KRAS mutations (G12V, G12R, and G12D) with PrimePCR products (Bio-Rad) for ddPCR (cat 1863115, 1863112, and 1863113) because these KRAS mutations encompass nearly 90% KRAS mutations in pancreatic cancer (12 (link)) (as shown in Figure 3a–d). Reactions were performed in 20 mL of reaction serum, which consisted of extracted DNA (5 mL), target primer mix (FAM) (1 mL), reference primer/probe mix (HEX) (1 mL), KRAS mutation droplet PCR supermix (10 mL), and distilled water (3 mL). PCR reactions were run on C1000 Touch thermal cycler incubating plates (Bio-Rad) at 95°C for 10 minutes followed by 40 cycles of 95°C for 15 seconds and 60°C for 60 seconds, followed by 10-minute incubation at 98°C. Negative controls without serum ctDNA showed no positive signal. All samples were analyzed in duplicate, and variations were set at <5%. The detection rate was set at >0.001%. Schematic and flowdiagram of digital PCR in EUS-guided FNA cytology and ctDNA specimen analyses is shown in Figure 1.