The word biomarker has different meanings to different physicians. A biomarker is defined as “a characteristic
that is objectively measured and evaluated as an indicator of normal biological processes, pathogenic processes, or pharmacologic
responses to a therapeutic intervention” by the National Institutes of Health Biomarkers Definitions Working
Group held in 1998. Thus, the definition of a biomarker may include routinely measured parameters in clinical practice
such as blood pressure and pulse or it could indicate a substances used in the diagnosis, treatment and monitoring of a disease.
Here, we discuss tumor biomarkers as an example of commonly used clinical biomarkers that impact patient diagnosis
and prognosis. In addition, a review of the limitations of common biomarkers and a highlight of emerging and promising
biomarkers are presented in the manuscript.
Keywords: Tumor, biomarkers, prognosis, predictive, validation, breast cancer, lung cancer, EGFR, intra-tumoral heterogeneity,
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