Figure 2.

Independent life cycle of tumors and tumor grade. The cycle of tumor progression may be involved in four key stages due to the genetic and epigenetic alterations: (1) Somatic cells are transformed and exhibit the traits of growth out of control, representing the benign stage; (2) Activation of somatic cell-ES/PGC-like cell conversion (including somatic cell-ES cell-like cell conversion and somatic cell-PGC-like cell conversion), which endows tumor with the capabilities of tumor initiation and metastasis, representing the entrance of malignant stage; (3) Activation of PGC-like cells undergo further development along with germ cell maturation to generate oocyte-like cells; (4) Parthenogenetic activation of oocyte-like cells generates to blastomere-like cells which can endow tumor with powerful abilities, such as asexual life cycle, pluripotency, immortality and therapeutic resistance, representing the terminal stages. Thus, the oocyte-like and preimplantation-like states allow for tumors to resist to therapy.