Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. The International Prognostic Index (IPI) is a clinical tool developed by oncologists to aid in predicting the prognosis of patients with aggressive non-Hodgkin's lymphoma. Prior to 1993, when the IPI was developed, the primary consideration in assessing prognosis was the Ann Arbor stage alone, but this was increasingly found to be an inadequate means of predicting survival outcomes, and so other factors were studied.