Table 2.

Recent studies evaluating the prognostic role of CTCs in advanced NSCLC. Abbreviations: NSCLC, non-small cell lung cancer; CTC, circulating cancer cell; chemo, chemotherapy; FISH, fluorescence in situ hybridization; PFS, progression-free survival; OS, overall survival; ISET, isolation by size of tumour cells; PD-L1, programmed cell death ligand 1; WBCs, white blood cells; PD-1, programmed cell death protein 1; NA, not applicable; vs, versus; EML4, echinoderm microtubule-associated protein-like 4; ALK, anaplastic lymphoma kinase; PD, progressive disease; Nivo, nivolumab; TKI, tyrosine kinase inhibitor; EGFR, epidermal growth factor receptor; RR, response rate; mo., months.

CTC Biomarkers	Study	Analysis Time-Point	Patients (n)	Detection Method	Therapeutic Approach	Main Findings
NA	J Li et al. [83]	At baseline, before 2 and 4 cycles of chemo, or after 1 and 2 mo. of targeted therapy	100	Negative enrichment of immune magnetic beads and FISH	Chemo /EGFR TKIs	Patients were divided into low CTC levels (<4 CTCs, LL) and high CTC levels (≥4 CTCs, HL). PFS: 5.6 mo. in LL group vs. 4.2 mo. in HL group, (p < 0.001).
	Alama et al. [84]	At baseline, after 4 and 8 cycles	89	ScreenCell CYTO	Nivolumab	OS in patients with ≤2 CTCs was 8.8 mo. vs. 6.2 mo. in patients with ≥2 CTCs (p = 0.05).
	Zhou et al. [85]	At the 1st and the 3rd cycle	59	CellSearch	Chemo	Pts with CTC ≥ 2 had a significant shorter PFS and OS (4.3 vs. 4.9 mo. and 8.3 vs. 11.2 mo., respectively)
PD-L1/PD-1	Ilié et al. [86]	At baseline	106	ISET® platform; Rarecells	Chemo	Trend for worse OS in patients receiving first-line cisplatin-based chemotherapy, whose tumours express PD-L1 in CTCs or immune cells
	Kallergi et al. [87]	At baseline and after 3 cycles	30	ISET® platform; Rarecells	Chemo	CTCs were detected in 93.3% and 81.8% of patients at baseline, and after the third chemotherapy cycle, respectively. The presence of >3 PD-1 + CTCs before treatment is associated with shorter PFS (0.5 vs. 3.9 months, p = 0.022)
	Cheng et al. [88]	At baseline	66	ISET® platform	NA	PFS time of initial treated patients with positive PD-L1 expression was shorter than that of those with negative PD-L1 expression in CTCs or tumour tissue (p > 0.05).
	Sinoquet et al. [89]	At baseline, or later, at progression	54	CellSearch	NA	CTCs and PD-L1(+) CTCs were detected in 43.4% and 9.4% of patients with NSCLC, respectively. PD-L1 expression concordance between tumour tissue and CTCs was low (54%). CTCs and PD-L1(+) CTCs were associated with worse OS, whereas PD-L1 expression in tumour tissue was not. Survival was worse in patients with PD-L1(+) CTCs
EGFR	Yang et al. [81]	At baseline and at day 28	68	CellSearch	Osimertinib	Patients in the favourable group (<5 CTCs) at baseline exhibited significantly longer PFS compared with patients in the unfavourable group (≥5 CTCs) (9.3 vs. 6.5 mo.; p = 0.0002).
ALK	Rossi et al. [90]	At baseline, at the end of first cycle of therapy (T1), and at the first and subsequent radiological assessments and/or at PD	199	CellSearch Expanded cytokeratins profile (EA)	NA	Pts with ≥4 CTCs had a significant lower PFS (0.29 vs. 0.66 years; p = 0.004) and OS (0.59 vs. 1.29 years, p = 0.04). Similar results using 5 CTCs as cut-off value. EML4-ALK(+) CTCs were associated with shorter PFS compared to NSCLC that did not express EML4-ALK in CTCs (0.57 years vs. 0.94 years, p = 0.017).
PD-L1, ALK, EGFR	Kulasinghe et al. [91]	At baseline	33	ClearCell FX	Nivo Chemo TKI	PFS was not found to be associated with CTCs prior to therapy (p = 0.0632), nor the presence of PD-L1 expression (p = 0.4023).
11 clinically relevant genes, including EGFR and ALK	Tamminga et al. [92]	At baseline	86	CellSearch	Chemo TKI	RR of patients with CTC were lower than in patients without CTC (OR = 0.22, p < 0.01). In both treatment groups, the difference in RR between patients with and without CTC was similar (interaction p = 0.17). No significant interaction between CTC presence and therapy was observed (p = 0.42 for PFS and p = 0.83 for OS).