Through the conversation analysis of interactions between medical oncologists gathered in a hospital in Italy, the article explores the functions that stories play in the diagnostic discussion of clinical cases. Results show that storytelling combines scientific and formal knowledge with anecdotal and experiential knowledge, integrating the two epistemic domains. Moreover, the stories, with their factual and normative format, mark fixed points and constitute evidence within an argumentative sequence that shapes the decision making as a logical consequence of the knowledge previously shared. During these conversations, doctors build a repertoire of guide-stories that constitutes a collective epistemic patrimony of the work community to be used for future diagnosis. Storytelling is described as a practice that answers to the need of a personalized medicine, that takes into account the specific features of each patient's particular situation.