NOTCH1 and neuroblastoma: Additionally, FZD6 (a Wnt receptor) positive NB cells are resistant to doxorubicin, form neurospheres, and express elevated levels of Twist1 and Notch receptor 1 (Notch 1) (mesenchymal markers),95 implying that FZD6 can be used as a marker of NB with stem cell properties.