In this paper, a new set of tumour phantoms for the experimental evaluation of Microwave Breast Imaging (MBI) as a method to diagnose breast cancer is presented. The phantoms were based on previously developed numerical models that had been clinically validated, supporting the appropriateness of the phantoms for the development of experimental systems. The proposed tumour phantom set was developed using polyurethane rubber with graphite and carbon-black powders and is the first to incorporate a large number of different shapes and levels of spiculation to emulate different levels of tumour malignancy. A series of spherical, non-spiculated targets was fabricated to model benign tumours, and a series of targets with irregular shapes and increasing spiculation was fabricated to model malignant tumours. The tumour phantoms can be combined with a variety of breast phantoms fabricated with the same method, which are unique in their diversity of glandular tissue content. The modular design of the phantom set allows for tumour and breast phantoms to be dynamically combined, creating an experimental test platform for MBI with a total of 154 cases. Moreover, the dielectric properties of the phantoms display good agreement with the literature, and the phantoms are constructed using materials that have demonstrated stable properties over time. Results also demonstrate how the shape and level of spiculation of a tumour can influence microwave reflections, and therefore impact the performance of imaging and diagnostic systems.