Progression-Free Survival (PFS) is a measurement used in oncology to assess cancer treatment effectiveness. It helps researchers and clinicians understand how long a patient lives without their disease worsening. This metric provides insights into how well a therapy controls tumor growth or spread, playing a role in evaluating new drugs and strategies.
Understanding Progression-Free Survival
Progression-Free Survival (PFS) refers to the duration a patient lives with cancer without the disease showing signs of worsening or growing. In this context, “progression” signifies that the cancer has grown, spread to new areas of the body, or a new lesion has appeared. PFS is measured from the start of treatment until disease progression is detected or death occurs from any cause.
PFS is distinct from “disease-free survival,” which measures the time after treatment when no detectable cancer remains in the body. Unlike overall survival, PFS specifically focuses on the period where the disease is kept under control by the treatment. It serves as an indicator of whether a therapy is successfully stabilizing the cancer, preventing it from advancing.
Significance of PFS in Cancer Treatment
PFS is important in oncology as it offers an early indication of a treatment’s effectiveness. In clinical trials, it helps researchers determine if a new drug or therapy halts or slows cancer progression. This is useful for treatments managing advanced, metastatic cancers where complete eradication may not be the immediate goal.
PFS can accelerate clinical trials compared to overall survival, as progression events often occur sooner than deaths. This allows faster evaluation of new therapies, potentially bringing beneficial treatments to patients more quickly. PFS also provides insights into a treatment’s direct impact on the disease, showing whether it controls tumor burden.
PFS also guides treatment decisions for individual patients, helping doctors assess how well a current therapy is working for a patient’s specific cancer. While PFS indicates disease stabilization, it does not always directly correlate with an improvement in a patient’s overall lifespan or their quality of life.
Measuring and Applying PFS
PFS is measured from the date a patient begins treatment or is randomized into a clinical trial. Disease progression assessment relies on imaging scans such as CT (computed tomography), MRI (magnetic resonance imaging), and PET (positron emission tomography). Blood tests for tumor markers and physical examinations also contribute to determining progression.
The criteria for defining disease progression are standardized, with the Response Evaluation Criteria in Solid Tumors (RECIST) widely used in clinical trials. Under RECIST 1.1 guidelines, progression is defined as at least a 20% increase in the sum of diameters of target lesions, with an absolute increase of at least 5 mm, or the appearance of new lesions. Target lesions are specific measurable tumors selected at treatment start, typically up to five lesions and two per organ, with a longest diameter of at least 10 mm. Lymph nodes are measurable if their short axis is 15 mm or more. These systematic evaluations monitor a patient’s response and identify when cancer has progressed.
PFS Alongside Other Treatment Outcomes
While Progression-Free Survival (PFS) measures the time a patient lives without cancer worsening, other outcomes provide different perspectives on treatment success. Overall Survival (OS) measures the total time a patient lives from a specific point, such as diagnosis or treatment initiation, until death from any cause. OS is a primary measure for evaluating new cancer therapies because it is an unambiguous endpoint.
Quality of Life (QoL) assesses a patient’s well-being and ability to perform daily activities during treatment. It considers physical, social, and psychological functioning, showing how a treatment affects a patient’s daily experience. While PFS indicates disease control, it does not automatically imply improved QoL, as treatments can have side effects.
PFS can serve as a “surrogate endpoint” for OS, especially in early clinical trials, allowing faster evaluation of new drugs because progression events occur sooner than deaths. An improvement in PFS is sometimes used to predict future OS improvement. However, the correlation between PFS and OS can vary depending on the cancer type and treatment, and PFS improvements do not always directly translate to longer overall survival. These outcomes—PFS, OS, and QoL—offer distinct insights into a treatment’s comprehensive benefit.