Disease staging systems play 2 critical roles in oncology. In the first instance, these systems summarize the extent of a patient’s cancer at the time of diagnosis and disease progression, by including information on the tumor characteristics at the primary site (eg, location, size, histologic features, etc) as well as locoregional (lymph node involvement) and distant metastatic state. Second, clinicians use these systems to evaluate treatment options, assess prognosis, and plan their patients’ care. Ideally, staging systems should have strong prognostic value so that clinicians can inform patients, with a reasonable degree of certainty, about the course of their disease and eligibility for adjuvant and therapeutic interventions.