Delineating the breast cancer immune microenvironment in the era of multiplex immunohistochemistry/immunofluorescence (mIHC/IF).

Breast cancer is the commonest malignancy and the leading cause of cancer death in females worldwide (1). Treatment is challenging especially for those that are triple negative. Increasing evidence suggests that diverse immune populations are present in the breast tumour microenvironment, which open up avenues for personalised drug targets. Historically, our investigations into the immune constitution of breast tumours have been restricted to analyses of one or two markers at a given time. Recent technological advances have allowed simultaneous labelling of over 35 markers, detailed profiling of tumour immune infiltrates at the single-cell level, as well as determining the cellular composition and spatial analysis of the entire tumour architecture. In this review, we describe emerging technologies that have contributed to the field of breast cancer diagnosis, and discuss how to interpret the vast datasets obtained in order to effectively translate them for clinically relevant use.