Tumor Initiating Cells, Cell Cycle Control and Cancer Stem Cells

A model depicting the hierarchical organization of the breast cancer tumor. A rare and primitive
breast cancer-initiating cell (BrCa-IC) maintains the breast cancer tumor. BrCa-IC possess high self-renewal
capacity; however, they can also mature or differentiate into breast cancer cells that have lost the ability
to sustain the tumor. Some of these cells may still possess extensive proliferative capacity indicative of a
progenitor cell, but have lost the ability to sustain the tumor after transplantation. The breast cancer cells
that comprise the bulk of the tumor tissue retain remnants of normal differentiation genetic programs.