PML and acute promyelocytic leukemia: Low dose of RA induces APL cells differentiation, but high dose of RA degrades PML‐RARa and induces PML‐nuclear body reformation and PML‐transformation related protein (Trp53) formation, leading to eradication of leukaemia‐initiating cells by senescence but not apoptosis in bone marrow of mice model APL.19, 51