The mammary gland is an organ comprised of branched ductal network terminated by secretory alveoli and embedded in mesenchymal stroma. Mammary alveoli, built by myoepithelial and epithelial cells with apico basal polarity, obtain their functional differentiation only during lactogenesis. For this reason they represent a good model for studies on differentiation process of epithelium.

Stem cells are cells with a capacity to self-renew and to generate daughter cells that can differentiate into different cell lineages to form all the cell types that are found in the mature tissue. The activity of mammary stem cells and their mitotic progeny is fundamental to normal mammary growth, differentiation and regeneration in successive cycles of pregnancy, lactation and involution. The isolation and characterization of mammary stem cells is fundamental to understanding mammary gland development and tissue homeostasis as well as breast oncogenesis.

In the last decade a progress has been achieved in understanding the mechanisms which control the cell death. Accumulating evidence suggest that apoptosis is not the only one type of pro- grammed cell death (PCD). Cells use different pathways to active self-destruction process. There are three types of programmed cell death (PCD): condensation prominent, type I or apoptosis, dependent on the activity of caspases, type II – autophagy prominent and type III occurring through disintegration of cells into fragments without condensation and involvement of lysosomal system.

ALCAM ( Activated Leukocyte Cell Adhesion Molecule ) / CD166 is a member of a small sub-group of transmembrane glycoproteins belonging to the immunoglobulin superfamily . The fully formed protein assigned to this group are characterized by the presence of three fragments : the extracellular międzybłonowego and a short cytoplasmic region . ALCAM/CD166 participates in heterophile ( ALCAM/CD166-CD6 ) and homofilnej ( ALCAM/CD166-ALCAM/CD166 ) in a variety of cell adhesion tissues and cell lines .

Most of the currently used anticancer drugs and radiotherapy induces apoptosis by DNA damage or inhibition of key enzymes involved in cell survival signaling pathways . This triggers a cascade of reactions leading to the activation of pro-apoptotic proteins Bcl- 2 family , such as Bad , Bid , Bax or Bak , forming a specific channel or coformation of megachannels ( mPTP ) in the outer mitochondrial membrane , allow the release of apoptogenic proteins , such as cytochrome c , Smac / DIABLO , AIF , Omi/HtrA2 , procaspase 9 and 3 and endonuclease G.