Biomarkers are substances that are either secreted by the tumor or produced by the body in response to the presence of cancer. Biomarkers serve as an objective measure for evaluation of normal and pathological processes as well as pharmacological responses to a therapeutic intervention. Cancer studies are usually difficult to interpret, especially based on the contemporary medical diagnosis. In this circumstance, biomarkers are developing as reliable diagnostic metabolites, which have many promising applications in oncological screening, differential diagnosis, risk assessment, response to treatment, and examining the progression of disease. Genome or protein based prognostic biomarkers are available, for numerous cancer types, for potential inclusion into clinical prognostic staging methods. However, there lies difficulty in translating these biomarkers into clinical outcomes. This review concerns important biomarkers related to wide varieties of cancer and also elucidates mode of action of few major biomarkers.