What is Progression Free Survival (PFS) in clinical trials?

Definition

Refers to the time from randomization (or the initiation of treatment in a single-arm trial) to tumor progression or death from any cause, whichever comes first.

Position

PFS is a tumor measurement-based endpoint that primarily evaluates the anti-tumor activity of a drug and, to a certain extent, considers the drug's safety and patient survival (accidental death). It is generally closely related to OS results. Some immunotherapies combined with chemotherapy in first-line non-small cell lung cancer clinical trials, as well as drugs like Sunitinib and Sorafenib in advanced renal cell carcinoma, have all been approved using PFS as the primary endpoint. However, FDA approval of PFS results has not been high in recent years, and drug approvals are usually based on OS results.

Advantages

Compared to OS, PFS generally requires fewer samples and shorter follow-up time. Studies are usually based on objective and quantitative assessments, and are not affected by cross-over and subsequent treatments, making them more reliable.

Disadvantages

Although PFS is highly correlated with OS, it may not necessarily translate into survival benefits. The evaluation of PFS requires frequent imaging assessments which may introduce assessment bias. More importantly, PFS results are influenced by the assessment interval. Different studies might have different definitions and censoring rules for PFS, so a clear definition is needed in advance.