Tumor heterogeneity represents extensive genetic and phenotypic differences among the same type of tumors in different patients (intertumor heterogeneity), and among cancer cells within a tumor (intratumor heterogeneity) (Fig. 1). In The populations of genetically distinct subclones can merge or be spatially separated.Such subclonal architecture varies dynamically during the disease course. The spatial separation of subclones in primary tumors could reflect physical barriers such as blood vessels or microenvironmental changes. Tumor subclones consist of cells that differ in clinically important phenotypic features and show differential gene expression due to the interplay between the genetic and epigenetic factors shaping the cellular phenotypes
