Colorectal cancer biomarkers: To be or not to be? Cautionary tales from a road well travelled

Table 1 Factors that can affect the outcome of biomarker studies

Analytical variables	Use of standard operating procedures for sample collection and processing
	Sample storage conditions (e.g., liquid nitrogen, -80  °C, aliquot size)
	Assay performance and reproducibility
Biomarker/biological variables	Biomarker stability (e.g., over time, under different storage conditions)
	Diurnal variation, fasting vs non-fasting
	Comorbidities, medications, diet
	Variability within a normal population
Cohort composition	Number of patients
	Inclusion/exclusion criteria for controls and patient selection
	Cohort balancing (e.g., age, gender matching)