Breast Cancer Intra-Tumor Heterogeneity: One Tumor, Different Entities.

In recent years, it has become evident that intra-tumor heterogeneity of breast cancer is a big challenge for the diagnosis, treatment, and clinical course of tumor-bearing patients. The advances in molecular biology and other technologies have led to the knowledge that a breast cancer tumor is comprised of multiple cellular entities. Here we review the two theories that have been described, trying to explain the origin of intra-tumor heterogeneity: clonal evolution and cancer stem cells.