Figure 1.

Mammosphere‐derived cells have stem‐cell characteristics. (a) Mammosphere structure (15 days’ growth). Mammosphere‐derived cells plated at clonogenic denstities can (b) generate mixed colonies, containing cells of all the three mammary lineage types (ductal epithelial, ESA, brown; myoepithelial, CD10, purple; alveolar, beta‐casein, red) or (c) generate complex structures in 3D Matrigel culture. (d) The structures clonally generated in vitro are functional, as demonstrated by beta‐casein secretion (immunostained red). Self‐renewal is demonstrated by serial passages of mammospheres.