Over the last 30 years, the academic community’s interest in the application of Microwave Imaging (MI) in the clinical diagnosis of pathologies and in the metabolic status of biomedical tissues has grown. Regarding breast cancer early diagnosis, microwave imaging is special because the electrical properties of breast tissues in the microwave spectrum are more sensitive and specific in discriminating pathological tissue from healthy tissue than other imaging techniques. This property reveals the potential of Microwave Tomography (MWT) to complement gold standard imaging techniques for the early diagnosis of breast cancer and other pathologies. In this work we present the evolution of equipment, prototypes and utility models that are being presented as systems for MWT. The most important components of the systems will be covered, such as sensor typology and architecture, sensing operation and data traffic, image formation methods and the main processing techniques. We conclude that although many types of microwave imaging hardware have been proposed in the last 3 decades, most setups have converged to three different types of antenna arrangement: circular, spherical and moving antennas arrangement. We examine the different types of hardware and analyze advantages and disadvantages of which one. We also go through existing clinical trials and provide a possible path forward for microwave imaging of the breast to overcome existing hurdles toward broader clinical acceptance.