Estimates Of Survival

Several estimates of survival have been developed to assess the efficacy of therapy and to describe prognosis in clinical cancer research. These include OS, disease-free survival (DFS), PFS, and EFS. OS is the gold standard for comparing therapeutic strategies, but has limitations because even in randomized trials patients often cross over to treatment offered in the opposing arm when discontinuing assigned therapy.

PFS, usually defined as time from start of therapy to disease progression or death,14 can serve as a surrogate for OS. EFS, which is the duration from start of therapy to predefined events such as disease progression or relapse, death, or serious toxicity, can also be used as an important endpoint. When EFS is defined from start of therapy to death from any cause or progression (whichever occurs earlier),1516 it is the same as PFS. On the other hand, time to progression (TTP)17 is usually measured from start of therapy to disease progression, with deaths due to causes other than progression not counted as an event, but censored at that time point.

Response duration, which is measured only in responding patients, also provides an estimate of drug efficacy. In myeloma, often only a subset of patients respond to a specific drug, and although TTP or PFS for the entire cohort may appear small, the benefit in responders may be substantial.1718

DFS applies only to patients achieving a CR, and refers to the duration from onset of CR to first evidence of relapse. Since it applies to only a small subset of patients with myeloma, it is probably not a good endpoint in this disease.

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