In the ALEX trial, a phase 3 RCT comparing first-line alectinib and crizotinib in ALK-positive NSCLC patients, elevated ctDNA levels in both treatment arms were associated with a reduced PFS (HR = 2.04 for alectinib and 1.83 for crizotinib) and a lower probability of survival (HR = 2.52 and 2.63, respectively) [76,84]. Here, ALK is linked to non-small cell lung carcinoma.