The clinical value of measuring health-related quality of life
Common clinical outcomes
Before the modern era of objectivity in clinical oncology research, reports of the effects of therapy were often based on an individual clinician's experience (case reports and series). As awareness of the advantages of research objectivity increased, several clinical outcomes, including overall survival, median survival time, tumor-free survival, progression-free survival, time to progression, and frequency and duration of tumor response, were accepted and widely used. Of these, overall survival is considered as being the “hardest” endpoint, i.e., least likely to be subject to misinterpretation, and tumor response the “softest” endpoint.,
In addition, the concept of levels of evidence was introduced.– The highest level of evidence, Level I, consists of data from meta-analysis of several phase III randomized controlled clinical trials (RCTs) or a very large, phase III trial containing several hundred patients. The lowest level of evidence, Level IV, is data derived from small, uncontrolled case series or reports. Currently, institutions collaborate with each other to enroll the large number of patients needed to produce Level I evidence, and eligibility criteria for patient enrollment are increasingly stringent in order to control as many clinical variables as possible.
The interpretation of clinical trials has been aided by the collection of toxicity data. As with response and survival data, there has been an attempt to become more comprehensive by collecting very detailed information with uniform grading systems.