Approved on Paper, Failing in Practice: The Surrogate Endpoint Problem Quietly Undermining Drug Development

In the architecture of modern drug approval, surrogate endpoints occupy a peculiar position. They are simultaneously a tool of scientific ingenuity and a source of growing institutional anxiety. A surrogate endpoint is, at its core, a measurable biological signal—a tumor shrinking on a scan, a cholesterol number falling, a viral load declining—that regulators accept as a stand-in for outcomes patients actually care about: living longer, functioning better, suffering less. The logic is pragmatic. Waiting years to confirm that a drug extends survival is slow and expensive. Measuring a biomarker shift takes months. For diseases with few options, speed is not merely convenient; it can be lifesaving.

But a widening body of evidence now challenges the premise that biomarker improvement reliably predicts meaningful clinical benefit. Across oncology, cardiology, neurology, and beyond, drugs that moved surrogate markers in the right direction have repeatedly failed to translate that movement into outcomes patients could feel. The gap between regulatory approval and real-world efficacy is not an occasional anomaly. Increasingly, researchers and clinicians are describing it as a structural feature of how the American drug development system operates.

What a Surrogate Endpoint Is—and What It Is Not

The U.S. Food and Drug Administration formally recognizes surrogate endpoints through two accelerated pathways: Accelerated Approval, established in 1992 in response to the AIDS crisis, and standard approval based on validated surrogates with established clinical correlations. The distinction matters. A validated surrogate—LDL cholesterol as a proxy for cardiovascular events, for instance—has demonstrated, through decades of data, a reliable relationship with patient outcomes. A surrogate accepted under Accelerated Approval may have a more speculative connection to benefit, one that post-market confirmatory trials are supposed to eventually verify.

The problem is that the verification step has historically been inconsistent. Confirmatory trials have been delayed, underpowered, or in some cases never completed. Drugs approved on biomarker data have remained on the market for years before adequate outcome data emerged—and in a number of high-profile cases, that data proved unflattering.

The oncology space offers some of the most instructive examples. Objective response rate—essentially, whether a tumor shrinks by a defined percentage—has been used extensively as a surrogate for survival benefit. Yet multiple analyses have found that tumor shrinkage correlates imperfectly with how long patients live or how their quality of life changes. A cancer that responds to treatment on a scan may recur quickly, or the treatment itself may carry toxicities that erode any functional gain. Patients and their oncologists, making decisions based on response rate data, are working from an incomplete picture.

The Accelerated Approval Paradox

Accelerated Approval was designed as a compassionate mechanism—a way to get promising therapies to patients with serious or life-threatening diseases before the full weight of clinical evidence had accumulated. By most accounts, it has fulfilled that mandate in meaningful ways, particularly in HIV and certain rare cancers. The pathway has enabled access to treatments that would otherwise have taken years longer to reach patients with no alternatives.

But the pathway's success created its own distortions. Pharmaceutical sponsors recognized early that surrogate-based approvals were faster, cheaper, and carried lower evidentiary bars than full approval. The incentive to pursue confirmatory outcome trials—trials that are longer, larger, and more expensive—weakened once market access was secured. Revenue flows before the hard question is answered. In some cases, the hard question was never seriously pursued.

A 2022 analysis published in JAMA Internal Medicine examined cancer drugs that received Accelerated Approval over a multi-decade period and found that a substantial proportion lacked confirmatory evidence of clinical benefit years after approval. Some had been voluntarily withdrawn; others remained available. The pattern prompted congressional scrutiny and, eventually, legislative changes under the Omnibus appropriations legislation of 2023, which granted the FDA clearer authority to require and enforce confirmatory trial timelines.

Whether those changes will be sufficient remains an open question.

When the Signal and the Outcome Diverge

Perhaps no therapeutic area has confronted the surrogate endpoint problem more publicly than Alzheimer's disease. The approval of aducanumab in 2021—granted over the explicit objections of the FDA's own advisory committee—centered on the drug's ability to reduce amyloid plaques in the brain. Amyloid reduction had long been theorized as a clinically meaningful marker, given the amyloid hypothesis of Alzheimer's pathogenesis. But the clinical trial data on cognitive benefit was deeply contested, and the FDA's decision to approve on the basis of plaque clearance alone drew sharp criticism from neurologists, bioethicists, and patient advocates alike.

The episode crystallized a tension that extends well beyond any single drug: the difference between a biomarker that correlates with a disease process and one that demonstrably predicts patient benefit. Amyloid plaques are associated with Alzheimer's. Reducing them is biologically plausible as a therapeutic goal. But plausibility and proof are not the same thing, and in a condition as complex as Alzheimer's—where patients and families are desperate for any intervention—the gap between the two carries enormous human weight.

Subsequent amyloid-targeting therapies have produced more encouraging clinical data, suggesting the hypothesis may yet yield meaningful treatments. But the aducanumab episode exposed how institutional pressure, commercial interest, and patient desperation can collectively push a surrogate endpoint past the evidentiary threshold it has actually earned.

The Structural Incentives That Perpetuate the Problem

Understanding why surrogate-based approvals persist despite their limitations requires looking beyond individual regulatory decisions to the broader architecture of drug development incentives. Sponsors face enormous financial pressure to reach the market quickly. Investors expect returns on timelines that full clinical outcome trials rarely accommodate. Patients with serious illnesses and their advocacy communities often support accelerated pathways, understandably prioritizing access over evidentiary completeness.

Regulators, meanwhile, operate under competing mandates. They are charged with ensuring safety and efficacy but also with facilitating access to innovation. In a political environment where drug approval speed is frequently scrutinized, the institutional risk of appearing to slow access to promising therapies is real and consequential.

The result is a system in which surrogate endpoints serve not merely as scientific tools but as negotiated compromises between competing pressures—pressures that do not always resolve in favor of the patient sitting across from a physician trying to make a treatment decision.

Toward More Rigorous Standards

Reforming surrogate endpoint standards does not require abandoning accelerated pathways. What it requires is more rigorous qualification of which surrogates have genuinely earned clinical trust, more enforceable timelines for confirmatory evidence, and greater transparency when the post-approval data fails to support the original approval rationale.

Some researchers have advocated for tiered surrogate classifications—distinguishing between biomarkers with strong clinical validation and those accepted on more speculative grounds—with distinct labeling and prescribing guidance for each. Others have called for outcome-based reimbursement structures that link payment to demonstrated patient benefit rather than biomarker response alone.

The FDA's recent regulatory actions suggest some institutional momentum toward tightening standards. But the deeper challenge is cultural and economic. As long as surrogate-based approval remains the path of least resistance to market entry, the pressure to pursue it will persist—and patients will continue to make treatment decisions based on data that tells only part of the story.

Science that advances medicine must ultimately answer to the patient, not the biomarker. Closing the gap between the two is among the most consequential challenges facing the life sciences field today.