['The cancer stem cell model implies a hierarchical organization within breast tumors maintained by cancer stem-like cells (CSCs). Accordingly, CSCs are a subpopulation of cancer cells with capacity for self-renewal, differentiation and tumor initiation. These cells can be isolated through the phenotypic markers CD44+/CD24-, expression of ALDH1 and an ability to form nonadherent, multicellular spheres in vitro. However, controversies to describe the stem cell model exist; it is unclear whether the tumorigenicity of CSCs in vivo is solely a proxy for a certain genotype. Moreover, in vivo evidence is lacking to fully define the reversibility of CSC differentiation.', 'In order to answer these questions, we undertook exome sequencing of CSCs from 12 breast cancer patients, along with paired primary tumor samples. As suggested by stem classical cell biology, we assumed that the number of mutations in the CSC subpopulation should be lower and distinct compared to the differentiated tumor cells with higher proliferation.', 'Our analysis revealed that the majority of somatic mutations are shared between CSCs and bulk primary tumor, with similar frequencies in the two.'] Does sequencing of breast cancer stem cell populations indicate a dynamic conversion between differentiation states in vivo?