Overall survival is still a gold standard for clinical trials, but is becoming a less reliable measure of drug efficacy because of the increase in treatment options, said David Cella, PhD, professor of medical social sciences at Northwestern University, Chicago, Illinois. If a patient’s disease progresses while on a drug, they can often take a second drug — which makes it harder to determine whether the first drug improved survival.

Progression-free survival avoids this issue by focusing on whether a patient’s disease advanced while on an experimental drug. But progression-free survival doesn’t guarantee that the drug extends or improves life — which is why it’s important to determine how well progression-free survival correlates with a patient’s quality of life.

“You’re making [patients] nauseated and tired and … causing problems with diarrhea or constipation,” said Dr Cella. “So how do you know if life is better just because you kept the tumor at bay?”

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An FDA analysis of 37 pivotal lung cancer trials — of which, 25 used PRO measures — underscores a major challenge in drawing conclusions from PROs: the methods used to collect, analyze, and report PROs vary from trial to trial.2 

“There was a wide range of analyses being performed for PROs and very few clear PRO research objectives driving these analyses,” wrote the FDA spokesperson in an email to Cancer Therapy Advisor.

One of the key issues the FDA analysis found is that most of the trials did not adequately account for missing data. The simplest way to handle missing PROs is to assume that the data are missing at random. But that is rarely true, said Dr Cella.