As the classical organoid field developed together with 3D cultures, much progress was being made in stem cell biology. In 1981, Evans and Kaufman (1981) established cultures of pluripotent stem cells from in vitro cultures of mouse blastocyts. In 1996, the first neurosphere cultures were characterized from mouse embryos (Reynolds and Weiss, 1996). In 1998, Thomson et al. (1998) established human blastocyst-derived pluripotent cell lines. In the mammary gland field, Max Wicha and Gabriela Dontu based methodologically on Reynold’s work (Reynolds and Weiss, 1996) designed an in vitro cultivation system that allowed the propagation of stem cells from human mammary gland and referred to them as mammospheres (Dontu et al., 2003). They showed the previously hypothesized existence of mammary progenitors capable of differentiating into luminal, myoepithelial, or both cell lineages. When single progenitor cells were cultured at low density in Matrigel, they developed into functional ductal/acinar structures. Thus, stem cells isolated either from embryos or from adult tissues could give rise to organoids. In 2009, Sato et al. (2009) used stem cells that express Leu-rich repeat–containing G protein–coupled receptor 5
