In the fertilized egg，a variety kinds of cells begin differentiation，and the differentiated different cells form the organs and finally form embryo taking the process of cell proliferation，migration，differentiation and apoptosis.In this sequence，cell differentiation is the final process of gradual transformation with formation of the specific structures according to their physiological functions and biochemical characteristics.Such biological phenomena result in the diversities between the cells in space dimension，showing different structures according to the developing phase.People becomes more and more clear to recognize that the cancer is not only the result of abnormal cell proliferation，but also the result of cell differentiation disorders at the stages of the tissue and organ developments，supposing that cancer is a kind of differentiation disorder caused by the impairment of normal function of the genes by wrong programs due to oncogenes and mutation of cancer suppressor genes.