Table 1.

Types of biomarkers based on their applications (80, 81).

Types of applications	Purpose	Examples	References
Diagnostic	•To detect or confirm the presence of a disease or a medical condition of interest. •Marks the foundation of precision medicine	Heat shock protein 70 (HSP70): These are network of molecular chaperons with folding catalyst which assist in protein folding. •Promote tumorigenesis by caspase dependent pathway mediated apoptosis suppression. •Expression of the gene significantly differ between control, leukoplakia and OSCC cases and within OSCC between different histological grades and are associated with progression to advanced stage tumor and nodal positivity. TP53 mutation early sign of HNSCC: TP53 tumour suppressor gene regulate cell growth and division, at the time of errors initiate apoptosis or senescence. •Mutation in TP53 cause invasive progression of lesions, a decrease in survival rate and a poor response to cisplatin and fluorouracil based chemoradiation, hence associated with local recurrence after therapy completion	(82, 83)
Prognostic	•A biomarker used to associate likelihood of a clinical event, disease progression, recurrence of a disease/medical condition •In clinical setup, it is routinely used to set trial entry and exclusion criteria for the stratification of high-risk population	NCBP2 and TFRC: High level of these proteins involved in regulating the proliferation, migration and invasion during the course of OSCC	(84)
Predictive	•A change in the biomarkers meant to anticipate the response of patients to a treatment or therapy	Ki-67: Nuclear protein, present in highly proliferating cells but disappear in resting phase of a cell. •Its level is predictive of relapse free and overall survival	(85)
Monitoring	•To assess the status of a disease or medical condition, through the course of the illness. •Change in the value helps predict status of the disease	Desmoglein-3: Preferentially maintains structural integrity in the oral epithelium. Keratin 13: Involved in regulating the differentiation of cells and play major role in carcinogenesis	(86, 87)
Response/pharmacodynamics	•A biomarker whose level changes in response to exposure to a medicine/therapy or an environment agent. •Highly useful in clinics and therapeutic development	Filamin-A(FLNA): Plays a major role in organization of extracellular network that assist in exchange of signals, control DNA double strand break response, cell-ECM interactions, cell signalling. •High expression of FLNA in the buccal squamous cell carcinoma (BSCC) patient tissue associated with poor survival -regarded as a novel biomarker for the diagnosis and outcome prediction of OSCC	(88)
Susceptibility/risk	•A biomarker which can be used to predict the changes of disease development in an apparently healthy individual. •Marks the basis of epidemiological studies on risk prediction	Fibrinogen gamma chain: Major function in homeostasis, significantly higher expression in OSCC compared to healthy controls. α-Defensins 1–3: Major constituent of azurophilic granules of neutrophils, not expressed in normal mucosa, their levels rise in physiological states to exhibit innate immune defenses against infectious diseases including epithelial cancers. •Acts as an important predictor linking inflammation, angiogenesis and cancer	(89, 90)