Herein, we report a case of a 21-year-old advanced lung adenocarcinoma patient with a low abundance (0.03%) of <i>EML4-ALK</i> rearrangement identified in plasma ctDNA upon progression on two lines of chemotherapy that demonstrated long-term complete response to alectinib (>13 months) including metastatic brain tumors. The gene discussed is ALK; the disease is lung adenocarcinoma.