Tumour Heterogeneity of Breast Cancer: From Morphology to Personalised Medicine.

Breast cancer (BC) displays striking clinical, morphological, and behavioural diversity within a single tumour and between tumours. Currently, mounting evidence indicates that the morphological heterogeneity of BC reflects an underlying spectrum of genetic and epigenetic portraits that control BC behaviour. Further understanding of BC heterogeneity will have an impact, not only on the routine diagnostic practices but also on patients' management decisions. Phenomena like diagnostic inconsistencies and therapeutic resistance, both primary and acquired, could be attributed, at least in part, to tumour heterogeneity within the same cancer and between the primary disease and subsequent recurrences. From a practical standpoint, and to minimise the impact of BC intratumoral heterogeneity, pragmatic approaches for adequate tumour sampling have been suggested in translational biomarker discovery and validation research studies and in the clinical setting. Here, we provide a brief overview of BC heterogeneity, with an emphasis on the clinical consequences of intratumoral heterogeneity.