The life span of cells is limited and dying cells are replaced with new ones, differentiated cells derived from stem . Stem cells in the adult organism can be detected markers present in both embryonic stem cells and stem cells in the tissues. Examples of the protein markers are : Oct3 / 4 , CXCR4 , Nanos , CD133 , CD34 . Common features of stem cells include: 1) the ability for self-renewal ( division created after the new stem cells ), 2 ) the ability to differentiate into specialized cells of tissues and organs, 3 ) resistance to stress and radiation toxicity . Stem cells are present in the adult organism different places , e.g., in the epidermis , gastrointestinal epithelium , and in skeletal muscle. The aggregates of cells called stem cell niches . They stopped there chemokinowymi systems . Chemokine known arrangement is in the bone marrow SDF- 1 ligand ( Stroma - derived factor 1) and the receptor CXCR4 on stem cells . Stressors may induce a decrease in SDF- 1 in the bone marrow , which causes the stem cells to the circulatory system and new niches . Another known system is the arrangement Wnt chemokine (ligand ) / Frizzle (LPR receptor complex ) on the surface of cells. The first direct evidence of the existence of cancer stem cells were observations of acute myeloid leukemia . Started isolating and descriptions of such cells in various tumors . Cancer stem cells are typically less than 1 % of tumor cells in murine models . It is understood that mutations in normal stem cells may lead to the transformation into cancer cells . A long period of interphase cancer stem cells promotes the accumulation of mutations in them , and resistance to toxic agents protects the cells against drugs.