Differentiation is a natural process by which cells become progressively more specialized to perform specific functions. Stem cells can, for example specialized to blood cells. In cancer, differentiated tumors mean how much mature (developed) cancer cells are in a tumor. Differentiated tumor cells resemble normal cells and tend to progress in a slower rate compared to the undifferentiated or poorly differentiated tumor cells.
Mature cells that perform a specific function in the body, for example, blood cells, bone cells, or skin cells, and are clearly different from other types of cell: see cell.
In the breast differentiated cells are those mature cells which make milk. Hormonal influences during the first full term pregnancy change the cells of the breast from immature to mature cells.