The chemical substance synthetic phosphoethanolamine (fosfoetanolamina sintética) was developed at the University of São Paulo (USP) in Brazil at the beginning of the 1990s and, until 2014, was tested on and distributed to cancer patients by members of USP’s Chemistry Institute (IQSC) in the city of São Carlos. That year, the production and distribution of ‘Fosfo’, as it became popularly known, was forbidden by IQSC’s director with the support of USP’s rector and the Brazilian National Sanitary Surveillance Agency (ANVISA). Shortly after this first prohibition, however, Fosfo gained popularity and became a national symbol of local scientific innovation and hope for a cancer cure. Likewise, it became an object of regulatory disputes involving multiple sectors of Brazilian society. Despite several further efforts by some scientists and patients to legitimate Fosfo as a pharmaceutical, ANVISA never authorized it. Nevertheless, at the same time as parts of Brazil’s established medical communities were becoming suspicious of Fosfo, its informal production and dissemination were increasing surreptitiously, with many Fosfo users and stakeholders questioning the legitimacy of conventional cancer therapies. In this article, I aim to understand the impact of Fosfo as a biotechnological innovation in terms of the ‘transfiguration’ of the physical and juridical persons involved in this controversy. Through the lens of transfiguration, the engagement and therapeutic-regulatory experiences of Fosfo users and stakeholders appear as deviant journeys that introduce discontinuities into established biomedicine and imply radical transformations at multiple levels, ranging from individuals to larger institutional environments.