Features of Cancer Stem Cells
肿瘤干细胞有干细胞的特征， 如自我更新、增殖和分化能力,多能(例如Sox2,Oct4、Nanog)和功能(例如ALDH1,CD133 +,CD34 + CD38 -)标记表达, 活跃的信号途径(例如切口,刺猬,Wnt),与干细胞相似的遗传和表观遗传结构, 和在体外形成球体的能力。把肿瘤干细胞注入免疫缺陷小鼠中，这些细胞通过自我更新和分化潜能，产生表型异质性肿瘤。肿瘤发生后，血管生成和侵袭和转移阶段，作为疾病进展的一部分。事实上，肿瘤干细胞通过血管相关因素的表达和通过EMT程序的诱导对转移的贡献，与诱导肿瘤血管化有关。他们对化疗和放射疗法的耐药性在临床上很重要，因为大多数抗癌药物都是针对肿瘤体积而不是肿瘤干细胞群。这些肿瘤干细胞的耐药能力可能与它们的慢循环表型有关，也可能与流出物转运体、抗凋亡蛋白、DNA修复机制或自由基清除剂的表达有关。
Figure 1: Characteristics of CSCs. CSCs are tumour-initiating cells that may result from malignant transformation of stem/progenitor cells, instigating the tumorigenic process. CSCs have been described to possess stem-like properties, such as self-renewal, proliferation and differentiation abilities, expression of pluripotent (e.g. Sox2, Oct4, Nanog) and functional (e.g. ALDH1, CD133+, CD34+CD38-) markers, active signalling pathways (e.g. Notch, Hedgehog, Wnt), genetic and epigenetic profiles similar to stem cells, and capacity to form spheres in vitro. CSCs can be efficiently detected when injected in immunocompromised mice, as these cells, through their self-renewal and differentiation potential, give rise to a tumour with phenotypic heterogeneity. Tumorigenesis is followed by angiogenesis and by the invasion and metastatic stages, as part of the disease progression. Indeed, CSCs have been associated with the induction of tumourvascularisation through the expression of vascular-related factors and by their contribution to metastasis through the induction of the EMT program. Their resistance to chemo and radiotherapies is clinically important as most anticancer agents target the tumour bulk but not the CSC population. The resistance ability of these cells may be associated with their slow-cycling phenotype, and/or expression of efflux transporters, anti-apoptotic proteins, DNA-repair mechanisms, or of free radicals scavengers.