Should you target a biomarker-positive population in your clinical trial, or simply track it?

Selecting a population with a higher response rate or more pronounced response can significantly enhance the likelihood of detecting an effective drug's treatment effect. This approach enables a study to demonstrate this effect with fewer participants than would be required in a non-targeted group.

This strategy is especially advantageous in early effectiveness studies as it offers clinical proof of concept that can inform broader studies.

In cases where only a small portion of patients, say 20%—a typical scenario in oncology—responds to treatment, targeting this subgroup can demonstrate effectiveness that might be obscured in a broader, unselected population.

The success of this enrichment strategy in reducing the necessary sample size for a study hinges on the prevalence of the biomarker and the drug’s relative effectiveness in both biomarker-positive and -negative groups.

The table below showcases the impact of focusing on marker-positive patients in clinical trials.

It presents the comparison of required sample sizes — how many more participants are needed in a general population versus a targeted, marker-positive group - under various conditions.

These conditions include differing prevalence rates of marker-positive patients and varying treatment effects in marker-negative patients (either 0% or 50% of the effect seen in marker-positive patients).

Sample Size Ratios as a Function of the Prevalence of Marker-Positive Patients
Source

The table operates under the assumption of flawless patient classification into positive and negative groups.

This strategic patient selection approach highlights the efficiency of precision medicine in clinical research.