Research in biotechnology and genetics is often characterised by its large research teams and its preoccupation for the commercialization of its foundings. This study examines the discovery of the two genes responsible for breast and ovarian cancers (BRCA1 et BRCA2) in the nineties. These genes were the first two to be identified in relationship with such a well-known and severe disease. Our goal is to understand the constitution of those large research teams, especially when firms are involved. Three dimensions are emphasized: first, the specificity of the research subject are very important; Second, researchers' strategy and objectives are a determining factor, when nearing major scientific breakthrough, networks were more unstable and conflicts more frequent; Third, the researchers' strategies could partly be explained by the set-ups, including the funding policies aspect.