Table 1.

Study quality questionnaire based on the assay methods and study design sections of the REMARK reporting recommendations for prognostic tumour markers [18]

Question	Yes = 1	No = 0
(1) Was the study prospective?	The study reports that patients and the performed test result were collected before the development of an outcome.	No report or clearly retrospective (e.g. patients with poor prognosis collected before biomarker measurement).
(2) Was evaluation of prognostic marker blinded to patient outcome?	The study reports an attempt to blind the person measuring the biomarker to patient outcome.	There is no such report, or assessor clearly not blinded.
(3) Was there a defined time period during which patients were enrolled?	Study defines time period, end of follow-up period, and median follow-up time.	Does not define criteria.
(4) Were there precisely defined clinical outcomes at the start of the study?	Study defines which clinical end points are to be measured.	No such definition.
(5) Were the methods for measuring the prognostic marker adequately described and referenced?	Clearly described and referenced	Not clearly described and referenced
(6) Cases unselected and unbiased?	No attempt to select patients with exclusion criteria	Only a subset of patients enter the study