Abstract
In this paper a novel approach to the development of the architecture of a knowledge-based decision support system for the management of patients with cancer of the breast is described. Its initial design and subsequent realization in a prototype version was facilitated by examining closely the overall clinical task and identifying its associated activities and related knowledge. Implementation in KEE highlights the value of rigorous conceptual modelling that leads to a design able to assess treatment response and disease progression as well as providing specific therapy advice. The approach is general and may be applied to the development of decision support systems for other areas of cancer and medicine.