EPHB6 and neuroblastoma: Treatment of NB cells with metformin or MIBG results in increased expression of genes encoding biomarkers of favorable outcome in NB (EFNB2, EFNB3, EPHB6, NTRK1, CD44 and MIZ-1) and tumor suppressor genes [early growth response 1 (EGR1), EPH receptor A2 (EPHA2), growth arrest and DNA-damage-inducible, beta (GADD45B), neuregulin 1 (NRG1), TP53 apoptosis effector (PERP) and sel-1 suppressor of lin-12-like (C. elegans) (SEL1L)]