Significance of postoperative follow-up of patients with metastatic colorectal cancer using circulating tumor DNA

Table 1 Characteristics of the markers used for the mutation analysis[16,17]

Marker	Exon number	Target codons	Size of PCR product (bp)	LOD (%)	DCE separation temperature (°C)
KRAS	2	12, 13	112	0.03	50
	3	59, 61	100	0.05	51
	4	117, 146	150	0.05	45
TP53	5	170-187	107	0.1	58
	6	187-224	169	0.5	52
	7	225-261	160	0.5	52
	8	262-307	151	0.03	56
APC	15	854-896	128	0.7	48
	15	1275-1308	100	0.7	48
	15	1290-1335	136	0.6	52
	15	1389-1446	174	0.3	48
	15	1430-1463	101	1	48
	15	1479-1530	156	1	51
	15	1539-1585	141	0.8	52
PIK3CA	9	542	106	0.2	48
	20	1025, 1031, 1047	136	0.3	49
BRAF	15	600	230	0.05	48
CTNNB1	3	45	152	0.4	52

bp: Base pair; DCE: Denaturing capillary electrophoresis; LOD: Limit of detection.

Table 2 Clinical patient data

Characteristics		Value
Number of patients		47
Age	mean, range (yr)	63.6 ± 12.3, 32-87
Gender	Female/male	16/31
Localization of primary	Rectum	13
	Colon	14
	Rectosigmoid	8
	Sigmoid	7
	Cecum	3
	Others	2
Localization of metastasis	Liver only	35
	Liver and/or other	12
Surgical treatment
Number of surgeries1		63
Synchronous mCRC	Combined (primary and liver)	12
	Primary before metastases	8
	Liver first	2
	Liver in the second stage	14
Metachronous mCRC	Liver	24
	Other metastases	3
Radicality	R0	40
	R1	7
	R2	16
Recurrence (R0 surgeries)	Number2	27
	Mean time to reccurence, range (mo)	9.0 ± 5.1, 3-22

¹Postoperative ctDNA was available for 50 surgeries.

²All parameters for recurrence evaluation were available for 22 R0 surgeries. mCRC: Metastatic colorectal cancer; R0: Complete resection; R1: Microscopically incomplete resection; R2: Macroscopically incomplete resection.

Table 3 Correlation of surgical radicality and postoperative circulating tumor DNA

	Number	State (time to recurrence or follow-up time)
R0	28
ctDNA positive	2	2 recurrence (6 mo)
ctDNA negative	26	10 no recurrence (6-36 mo), 14 recurrence (4-22 mo)1
R1	7
ctDNA positive	4	4 recurrence (3-7 mo)
ctDNA negative	3	1 no recurrence (5 mo), 2 recurrence (7 or 22 mo)
R2	15
ctDNA positive	15	12/2/1 metastasis/primary tumor/both present
ctDNA negative	0	-

¹In two ctDNA negative R0 surgeries were missing follow-up information. ctDNA: Circulating tumor DNA; R0: Complete resection; R1: Microscopically incomplete resection; R2: Macroscopically incomplete resection.

Table 4 Comparison of circulating tumor DNA and standard detection methods

Number of recurrences	ctDNA	Imaging methods	CA19-9 and/or CEA markers
13	+	+	+
3	+	+	-
2	+	-	+
4	+	-	-

Plus and minus symbols indicate positive and negative results of screening for recurrence, respectively. CA 19-9: Carbohydrate antigen 19-9; CEA: Carcinoembryonic antigen; ctDNA: Circulating tumor DNA.