Genred documents facilitate collaboration and workplace practices in many ways--particularly in the medical workplace. This article represents a portion of a larger grounded investigation of how medical professionals invoke a wide range of rhetorical strategies when deliberating about complex patient cases during weekly, multidisciplinary deliberations called Tumor Board meetings. Specifically, the author explores the role of one key document in oncological practice, the Standard of Care document. Each Standard of Care document (one for every known cancer) presents a set of national guidelines intended to standardize the treatment of cancer. Tumor Board participants invoke these guidelines as evidence for or against particular future action. In order to better understand how genred, generalizable guidelines like Standard of Care documents afford decision making amid uncertainty, the author conducts a temporal and contextual analysis of the document's use during deliberations as well as a modified Toulminian analysis of a representative sample. Results suggest that, while on its own the document achieves an authoritative, charter-like purpose, it fails to make explicit a link between individual patients' experiences and the profession's expectations for how to act. Implications for how genred, generalizable guidelines--given the way they encourage certain ways of seeing over others--organize and authorize work are discussed, and a modified Toulminian approach to understanding the relationship between claim and evidence in multimodal texts is modeled. (Contains 8 figures, 5 tables and 4 notes.)