With effective obesity drugs widely available, patients in trials quickly realize they are on placebo and drop out, compromising data integrity. This is pushing the industry toward using existing drugs as the control arm, making trials more complex and expensive but yielding more realistic, comparative data on efficacy and tolerability.

The PROTEUS trial used ADT plus surgery as its control, not surgery alone. This design is controversial because many patients choose surgery specifically to avoid systemic therapies like ADT. This complicates the interpretation of results and reflects a disconnect from real-world patient motivations.

Contrary to common belief, centralized radiology review isn't always superior. In blinded trials, local radiologists with specialist knowledge and clinical context can be as, or more, accurate. The PROTEUS trial's investigator-assessed Metastasis-Free Survival (MFS) showed an even stronger treatment effect (HR 0.74) than the blinded central review (HR 0.80).

The practice-changing KEYNOTE-689 trial was open-label, meaning patients knew their treatment. This could introduce bias; patients on the standard care arm may have dropped out ("bailed"), while those on the pembrolizumab arm might have progressed, artificially making the rates of patients reaching surgery appear similar.

Clinicians identify outdated control arms—like single-agent chemotherapy without newer targeted agents—as a major deterrent for patient trial participation. Patients are unwilling to be randomized to a therapy that doesn't reflect the current, more effective standard of care. This pressure is forcing sponsors and the FDA to design trials with more realistic comparator arms.

The control arm in the EMBARK study was blinded to PSA results, preventing physicians from intervening with standard-of-care AR antagonists at PSA progression. This design likely delayed subsequent effective therapies, making the control arm underperform and potentially exaggerating the overall survival benefit of the experimental arms.

Learning from Karuna, Seaport actively combats the high placebo effect in psychiatric trials. Their strategy involves specific design tactics, such as optimizing the frequency of clinician assessments and using a single treatment arm, to minimize both therapeutic interaction and patient expectation bias, which are known drivers of placebo response.

Many clinical trials fail not because the science is wrong, but because of operational issues like patient recruitment and retention. These problems often stem from overly burdensome and rigid trial designs that deter participation, a preventable error.

The highly anticipated PROTEUS trial is testing a new drug combination against a control arm of ADT plus placebo for prostatectomy patients. This design is controversial because ADT is not standard care in this setting, raising concerns that a positive result could be driven by a suboptimal control arm.