ENO2 and neoplasm: The extensively studied tumor-specific proteins are carcinoembryonic antigen (CEA) [68], alpha-fetoprotein (AFP) [69], PSA [70], chorionic gonadotropin (HCG) [71], carbohydrate antigen 19 − 9 (CA19-9) [72], carbohydrate antigen 12 − 5 (CA12-5) [73], carbohydrate antigen 72 − 4 (CA72-4) [74], carbohydrate antigen 24 − 2 (CA24-2) [75], carbohydrate antigen 15 − 3 (CA15-3) [76], cytokeratin 19 fragment (CYFRA21-1) [77], neuron-specific enolase (NSE) [78], and squamous cell carcinoma-associated antigen (SCC) [79].