As shown in microscopy images and in the quantitative evaluation of the spheroid diameters reported in Fig. 1D, while p27 expression reduces the dimension of glioblastoma spheres, G9R‐p27 tumoroids increase in size statistically and significantly compared with wt‐p27‐ or vehicle‐derived colonies after 6 days from seeding. Here, CDKN1B is linked to glioblastoma.