Thirty-nine patients treated with anti-PD-1/PD-L1 agents as second- or third-line therapy were enrolled...Patients were divided into 3 groups: no CTC detectable (CTCnull, n = 15), PD-L1 positive CTC (CTCpos, n = 13), and PD-L1 negative CTC (CTCneg, n = 11)....PD-L1 expression on CTCs is a promising biomarker in patients with NSCLC treated with ICIs.