Tumoral heterogeneity of breast cancer

The objective of this literature review is to describe the types of tumor heterogeneity in breast cancer and their clinical implication. Two kinds of tumor heterogeneity are described: intertumor heterogeneity and intra-tumor heterogeneity. In breast cancer, inter-tumor heterogeneity was best characterized in the 2000s thanks to high throughput analyses. These analyzes resulted in a molecular classification of breast cancers distinguishing four subtypes: Luminal A, Luminal B, HER 2+ and basal like. This variability may be observed between the primary tumor and metastases, namely the temporal intratumor heterogeneity. The average discrepancy for the progesterone receptor, estrogen, and between HER2 status appears to be 33%, 20% and 8%, respectively. It is then interesting to study the heterogeneity within the primary tumor: this spatial intra-tumor heterogeneity is poorly known. Physiopathology of intra-tumor heterogeneity light be deciphered by studies on cancer stem cells and clonal evolution model. In addition, the tumor microenvironment seems to actively contribute to this heterogeneity. The major interest to study this heterogeneity is the clinical implication that could result. While precision medicine is emerging, it is important to capture the heterogeneity of each specific tumor type. These new biological knowledge will allow us to anticipate such heterogeneity and individualize the management of breast cancer.