What Are PFS, the Time Until Cancer Worsens, and Second PFS or PFS-2, Increasingly Used in Recent Years?

What Is Progression-Free Survival (PFS)?

Progression means "advancement" or "worsening," and progression-free survival literally means a life span without progression. It is one of the most commonly used terms in oncology. Progression-free survival is the time from a new treatment until cancer progression is detected, and indicates how long treatment keeps the cancer under control. In a clinical trial, measuring progression-free survival is a way to see how well a new treatment works. PFS is the abbreviation. It is generally expressed in "months".

What Is Overall Survival?

Overall survival is the time elapsed from either the date of diagnosis or the start of treatment for a disease such as cancer in patients diagnosed with the disease. In a clinical trial, measuring overall survival is the best way to see how well a new treatment works. The English term is "overall survival"; the abbreviation OS is used. It is generally expressed in "months".

- Related topic: Why Are Cancer Clinical Trials Important? What You Need to Know

What Is Second Progression-Free Survival (PFS-2)?

It is a new measure of survival and efficacy for patients with cancer.

Overall survival (OS) remains the preferred endpoint and the most important measure of efficacy for assessing sustained clinical benefits in oncology studies. In some circumstances, using overall survival as a study objective may be problematic because of the assessment of study design, multiple lines of treatment, long survival times, and other factors. In this context, new-generation immunotherapies and targeted drugs with more moderate side-effect profiles require a new and more appropriate study endpoint. Current studies suggest that second progression-free survival (PFS2) may be a suitable endpoint for this purpose.

The European Medicines Agency (EMA) recommends using PFS2 to help understand the significance of meaningful improvements in PFS when overall survival cannot be measured. PFS2 is defined as the time from a patient's enrollment in a clinical trial to tumor progression during the next line of treatment or death from any cause.

A Study Demonstrating the Importance of PFS2

In 2014, Blood published a study in which researchers searched clinictrials.gov for cancer trials that included PFS2 as an endpoint (search terms: cancer and PFS; cancer and PFS2).

As of July 2014, a total of 7,957 cancer studies listed PFS as a study endpoint; 14 of these included PFS2. Every study including PFS2 also already listed PFS as an endpoint. PFS was the primary endpoint in 13 of these 14 studies. Overall survival was not the primary endpoint in any trial listing PFS2, but was a secondary endpoint in 13 of the 14 trials.

The types of oncology studies evaluating PFS2 in this analysis included multiple myeloma (3 studies), prostate cancer (2 studies), breast cancer (2 studies), head and neck cancer (1 study), colorectal cancer (4 studies), non-small cell lung cancer (1 study), and pancreatic cancer (1 study). The analysis identified several issues relating to the inclusion of PFS2 in clinical trials. First, it is a new concept for healthcare professionals. For sponsors funding clinical trials, PFS2 results need to be communicated clearly and in a clinically meaningful way, and the data should be incorporated into medical and economic models.

In conclusion, PFS2 is emerging as a secondary endpoint in an increasing number of clinical oncology studies evaluating the benefits of sequential cancer treatments. Although the data are currently limited, results from a growing number of studies will help determine how PFS2 in advanced cancer provides additional and complementary information about the efficacy of sequential treatments.