Introduction

The goal of lymphoma therapy is to improve the outcome of patients by reducing the size of or completely eradicating the disease, and/or by causing a decrease in disease-related symptoms. Although major progress has been made in the treatment of patients with lymphoma, many still fail to achieve a response or subsequently relapse. Thus, new therapies are needed to improve patient outcome. In order to identify promising regimens and reliably compare the results with existing therapies, it is critical to have uniform definitions of the extent of disease prior to therapy and measurements of efficacy following treatment. In the absence of active agents, response criteria are irrelevant. However, because of the increasing number of effective treatment options for lymphoma, standardized response criteria are necessary to assess and compare the activity of various therapies within and among studies, and facilitate the evaluation of new treatments by regulatory agencies.

In 1999, an international working group (IWG) of clinicians, radiologists, and pathologists with expertise in the evaluation and management of patients with lymphoma developed guidelines that standardized a number of important components of patient assessment. Since response is most often measured by the change in size of lymph nodes, the first goal was to define the size of a “normal” node, which previously had varied widely among studies. Even minor variations in what is considered “normal” lymph node size can result in major differences in the complete response rate following therapy.