PHOX2B and neoplasm: Circulating tumor cells (e.g., cell markers such as GD2), specific genetic alterations in cell-free DNA (e.g., MYCN, ALK, C-Circles), mRNAs (e.g., TH, PHOX2B and DCX), and more recently, hypermethylation (e.g., RASSF1A) and extracellular vesicles, also seem of interest for defining prognosis and detecting early relapses and minimal residual disease [38,39,40,41].