Abstract
This article aims to understand why medical actors recently published lists of rare and very rare cancers. It studies four lists of rare and very rare cancers based on interviews with the main actors on these lists and an analysis of medical articles in which these lists were published. It argues that these lists constitute boundary objects whose aim is to deal with the organizational challenges raised by precision medicine, which imply increasing the coordination work between various types of actors. Our work therefore allows a better understanding of the functioning of the recursive standardization process of a boundary object and, by analyzing how the category of rarity is built at the intersection of both professional and nosographic principles, shows the intertwining of the biomedical, organizational, and political aspects on which rests the practice of contemporary precision medicine.