MYCN and neuroblastoma: Although metronomic topotecan and vinblastine are the chemotherapeutic drugs that have been most frequently used in preclinical models of neuroblastoma, other metronomic therapeutic approaches have been tested with metronomic cyclophosphamide (mCTX) at the dose of 40 mg/kg/day p.o. in SH-SY5Y (chemotherapy-sensitive, non-MYCN-amplified) and SK-N-BE2 (chemotherapy-resistant, MYCN-amplified) tumor xenografts.