Response rates--an evolution.

The documented frequency of response of cancers to common chemotherapy agents and combinations appears to have decreased over the decades. Multiple reasons exist for this decline including: changes in eligibility and evaluability criteria; changes in the type of patients entered onto trial; and, altered criteria for response and methods for response assessment. The disinclination to publish negative results also permits a bias in a favor of overestimating a drug's efficacy. Circumspection now is advised in assessing data from older trials.