Over the past few decades, the US Food and Drug Administration (FDA) has increasingly relied on surrogate measures such as blood tests instead of clinical outcomes for medication approvals. But critics say the agency lacks consistent standards to ensure the surrogate aligns with clinical outcomes that matter to patients — things like improvements in symptoms and gains in function.
Sometimes those decisions backfire. Consider: In July 2021, the FDA approved aducanumab for the treatment of Alzheimer’s disease, bucking the advice of an advisory panel for the agency that questioned the effectiveness of the medication. Regulators relied on data from the drugmaker, Biogen, showing the monoclonal antibody could reduce levels of amyloid beta plaques in blood — a surrogate marker officials hoped would translate to clinical benefit.
The FDA’s decision triggered significant controversy, and Biogen in January announced it is pulling it from the market this year, citing disappointing sales.
Although the case of aducanumab might seem extreme, given the stakes — Alzheimer’s remains a disease without an effective treatment — it’s far from unusual.
“When we prescribe a drug, there is an underlying assumption that the FDA has done its due diligence to confirm the drug is safe and of benefit,” said Reshma Ramachandran, MD, MPP, MHS, a researcher at Yale School of Medicine, New Haven, Connecticut, and a coauthor of a recent review of surrogate outcomes. “In fact, we found either no evidence or low-quality evidence.” Such markers are associated with clinical outcomes. “We just don’t know if they work meaningfully to treat the patient’s condition. The results were pretty shocking for us,” she said.
The FDA in 2018 released an Adult Surrogate Endpoint Table listing markers that can be used as substitutes for clinical outcomes to more quickly test, review, and approve new therapies. The analysis found the majority of these endpoints lacked subsequent confirmations, defined as published meta-analyses of clinical studies to validate the association between the marker and a clinical outcome important to patients.
In a paper published in JAMA, Dr. Ramachandran and her colleagues looked at 37 surrogate endpoints for nearly 3 dozen nononcologic diseases in the table.
Approval with surrogate markers implies responsibility for postapproval or validation studies — not just lab measures or imaging findings but mortality, morbidity, or improved quality of life, said Joshua D. Wallach, PhD, MS, assistant professor in the department of epidemiology at the Emory Rollins School of Public Health in Atlanta and lead author of the JAMA review.
Dr. Wallach said surrogate markers are easier to measure and do not require large and long trials. But the FDA has not provided clear rules for what makes a surrogate marker valid in clinical trials.
“They’ve said that at a minimum, it requires meta-analytical evidence from studies that have looked at the correlation or the association between the surrogate and the clinical outcome,” Dr. Wallach said. “Our understanding was that if that’s a minimum expectation, we should be able to find those studies in the literature. And the reality is that we were unable to find evidence from those types of studies supporting the association between the surrogate and the clinical outcome.”
Physicians generally do not receive training about the FDA approval process and the difference between biomarkers, surrogate markers, and clinical endpoints, Dr. Ramachandran said. “Our study shows that things are much more uncertain than we thought when it comes to the prescribing of new drugs,” she said.