Park 2009.

Study characteristics
Patient sampling	Country Korea Study design Prospective Setting Hospital Dates of data collection N/R Population (n) 1707 Inclusion criteria curative resection for colorectal cancer followed by surveillance programme Exclusion criteria Patients with synchronous metastatic disease or patients undergoing palliative resection, and those with carcinoma in situ, inflammatory bowel disease, familial adenomatous polyposis or pathology other than adenocarcinoma were excluded, as were patients with T1 cancer treated by endoscopic mucosal resection or transanal excision. In addition, patients with chronic obstructive lung disease, chronic liver disease, peptic ulcer, and diabetes were excluded. Participants Included (n) 1263
Patient characteristics and setting	Age range 61 (21 ‐ 90) Smoking status N/R Site of primary tumour Colon 631, rectum 632 Stage of primary tumour I 212, II 514, III 537 Perioperative investigations done to ensure no residual disease N/R Chemotherapy/radiotherapy? Yes, but not specified Recurrences (n) 291 Site of recurrences N/R
Index tests	CEA timing per schedule CEA technique N/R CEA threshold 7 µg/L Definition of positive 1 elevated value Which CEA value (s) used? All, although at point of recurrence for 18.8%
Target condition and reference standard(s)	Follow‐up schedule 2‐ or 3‐ month intervals for the first 2 years and at 6‐month intervals thereafter. At each visit, CEA levels are assayed, a full history is obtained, and a physical examination is per‐ formed. A serum CEA assay is performed with at least a 2‐ week interval after the administration of chemotherapy. Colonoscopy is performed within 6 months to 1 year following surgery, and every 3years thereafter. Chest radiographs and abdominopelvic computed tomography (CT) are performed 6 months postoperatively and then at yearly intervals. Unscheduled CT or positron emission tomography (PET) scans were performed on patients with increased serum CEA concentrations or patients who were symptomatic. Reference standard diagnosis of a tumour recurrence was confirmed by biopsy or examination of the resected specimen. Other‐ wise, tumour recurrence was documented from the first clinical or radiologic sign of disease that showed an unrelenting course leading to tumour progression and/or death. The criteria for establishment of recurrent disease included histologic confirmation, palpable disease, or radiographic evidence of disease with subsequent clinical progression and supportive biochemical data, particularly an increased CEA level.
Flow and timing	Timing of CEA vs reference standard (days) per protocol
Comparative
Notes
Methodological quality
Item	Authors' judgement	Risk of bias	Applicability concerns
DOMAIN 1: Patient Selection
Was a consecutive or random sample of patients enrolled?	Unclear
Did the study avoid inappropriate exclusions?	No
		High	Low
DOMAIN 2: Index Test All CEA thresholds
If a threshold was used, was it pre‐specified?	Yes
Is the same method and instrument used for all CEA measurements?	Unclear
Is there an estimation of reproducibility of the method, for example the % coefficient of variation at specific concentrations?	No
Is there an indication of method accuracy, for example, is there evidence of participation in an external quality assessment and proficiency testing scheme?	No
		Unclear	Low
DOMAIN 3: Reference Standard
Is the reference standards likely to correctly classify the target condition?	Yes
Were the reference standard results interpreted without knowledge of the results of the index tests?	No
		Low	Low
DOMAIN 4: Flow and Timing
Did all patients receive the same reference standard?	Yes
Were all patients included in the analysis?	No
Was the index test repeated prior to the reference standard?	No
Was the the timing between index test(s) and reference standard ascertainable?	No
Did all patients receive a reference standard?	Yes
		High