Table 2. Association between serum CEA and CTCs.

	CTC negative	1-2 CTCs/sample	≥ 3 CTCs/sample
CEA normal N = 116 (0–5 ng/mL)	103 (89%)	11 (10%)	2 (1%)
CEA increased N = 65 (>5 ng/mL)	37 (56%)	16 (24%)	12 (18%) p < 0.001a
Median CEA (ng/mL) (IQR)	2.91 (2.04–3.41)	6.71 (2.77–15.3)	13.4 (6.59–24.8) 0 versus 1–2 p < 0.001b 0 versus ≥ 3 p < 0.001b 1–2 versus ≥ 3 p = 0.49b

CEA = Serum carcinoembryonic antigen; CTC = Circulating tumour cell

^aChi-squared,

^bMann–Whitney test