Monitoring of treatment response has also been reported in anti-EGFR treated CRC using KRAS mutations [40], TKI-treated lung cancer for EGFR del19/L858R [41], BRAF mutated melanoma [42] and gynecologic malignancies [43] and detection of progression on primary TKI in ctDNA has been reported in EGFR mutated NSCLC [44] and CRC [45]. Here, KRAS is linked to melanoma.