Breast tumor heterogeneity: causes and consequences

In breast and other cancer types, a high degree of diversity exists among and within tumors. Breast tumors are composed of a variety of cancer cells with distinct phenotypes and genotypes. The molecular mechanisms responsible for this intratumoral heterogeneity are not well defined. Two currently popular hypotheses that attempt to explain intratumoral heterogeneity are the cancer stem cell and the clonal evolution models. Each of these concepts has been investigated for some time, leading to the accumulation of findings that support one or the other. Although the two views share some similarities, they are fundamentally different notions with very different implications for clinical practice.