ENO2 and neoplasm: Traditionally, several plasma, serum, and urine markers have been evaluated as predictors of tumor progression in NETs, including 5-hydroxy indole acetic acid (5-HIAA), chromogranin A (CgA), serotonin, neuron-specific enolase (NSE), neurokinin A, E-cadherin, or neuropeptide K [16].