MKI67 and neoplasm: By tracking the xenografts-derived cells through immunohistochemistry for human nuclei (hNuc), we confirmed that U87 cells (Figs. 1E1, S1A) remain confined within the macroscopic tumor boundaries (arrowheads in Fig. 1E1) and are highly proliferative, as evidenced by the co-localization of hNuc with Ki67 proliferation marker (arrows in Figs. 1E1 and S1A–C).