An update on criteria for assessing tumor response to treatment.

Standardized tumor response criteria have been developed over time since the advent of cytotoxic anticancer therapies. The criteria have evolved and continue to do so as the understanding of the therapeutic basis of various anticancer agents increases and as novel therapeutic agents are developed. Currently, the criteria can be divided into the following main categories: anatomical-based criteria; tumor- and therapy-specific criteria; metabolic-based criteria; and response assessment of lymphomas. The standardized criteria are critical to the successful conduct of clinical trials during the development of cancer therapeutic agents as they offer uniform end points that facilitate comparison of therapeutic agents and interpretation of studies. The criteria are also relevant in clinical practice as they standardize how radiologists select, measure, and report lesions in oncology patients, and they provide standardized definitions for tumor response categories. To remain relevant in a rapidly evolving oncology field and provide up-to-date imaging information that meets the needs of oncologists in both research trials and clinical practice, radiologists need to familiarize themselves with the various standardized tumor response criteria.