Introduction
A variety of endpoints may be measured and reported from clinical studies in
oncology. These may include total mortality (or survival from the initiation
of therapy), cause-specific mortality, quality of life, or indirect surrogates
of the four outcomes, such as event-free survival, disease-free survival, progression-free
survival, or tumor response rate. Endpoints may also be determined within
study designs of varying strength, ranging from the gold standard—the
randomized, double-blinded controlled clinical trial—to case series
experiences from nonconsecutive patients. The PDQ editorial boards use a
formal ranking system of levels of evidence to help the reader judge the
strength of evidence linked to the reported results of a therapeutic strategy.
For any given therapy, results can be ranked on each of the following two
scales: (1) strength of the study design and (2) strength of the endpoints.
Together, the two rankings give an idea of the overall level of evidence.
Depending on perspective, different expert panels, professional organizations,
or individual physicians may use different cut points of overall strength of
evidence in formulating therapeutic guidelines or in taking action; however,
a formal description of the level of evidence provides a uniform framework for
the data, leading to specific recommendations.
The PDQ Adult Treatment Editorial Board and the PDQ Pediatric Treatment Editorial Board add information on levels of evidence,
described below, to the PDQ Adult Cancer Treatment Summaries and the PDQ Pediatric Cancer Treatment Summaries when appropriate.
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