[When a metastasis hides another]

Breast cancer is one of the leading causes of death in women. There are many different entities, both morphologically and immuno-histochemically or genomically. Intra-tumour heterogeneity can be defined in time (temporal heterogeneity) and in space (spatial heterogeneity) and is influenced by both internal and external factors, such as genetics, epigenetics, host response, possible treatments or the tumour microenvironment. The detailed analysis of these multiple interactions could help to develop new therapeutic targets.