MKI67 and neuroblastoma: Moreover, tumour morphology, Ki-67 proliferative index (Fig. EV4D,E) and tumour immunohistochemical staining for PHOX2B (neuroblastoma) and CD99 (Ewing sarcoma) remained unchanged between tumours generated from non-bioprinted and bioprinted cells (Fig. 5Bii,Cii).