An Overview of Cancer Drugs Approved by the US Food and Drug Administration Based on the Surrogate End Point of Response Rate

Defining subpopulations of differential drug response to reveal novel target populations

Personalised medicine has predominantly focused on genetically altered cancer genes that stratify drug responses, but there is a need to objectively evaluate differential pharmacology patterns at a subpopulation level. Here, we introduce an approach based on unsupervised machine learning to compare the pharmacological response relationships between 327 pairs of cancer therapies. This approach integrated multiple measures of response to identify subpopulations that react differently to inhibitors of the same or different targets to understand mechanisms of resistance and pathway cross-talk. MEK, BRAF, and PI3K inhibitors were shown to be effective as combination therapies for particular BRAF mutant subpopulations. A systematic analysis of preclinical data for a failed phase III trial of selumetinib combined with docetaxel in lung cancer suggests potential indications in pancreatic and colorectal cancers with KRAS mutation. This data-informed study exemplifies a method for stratified medicine to identify novel cancer subpopulations, their genetic biomarkers, and effective drug combinations.

The use of validated and nonvalidated surrogate endpoints in two European Medicines Agency expedited approval pathways: A cross-sectional study of products authorised 2011-2018

BACKGROUND

In situations of unmet medical need or in the interests of public health, expedited approval pathways, including conditional marketing authorisation (CMA) and accelerated assessment (AA), speed up European Medicines Agency (EMA) marketing authorisation recommendations for medicinal products. CMAs are based on incomplete benefit-risk assessment data and authorisation remains conditional until regulator-imposed confirmatory postmarketing measures are fulfilled. For products undergoing AA, complete safety and efficacy data should be available, and postauthorisation measures may include only standard requirements of risk management and pharmacovigilance plans. In the pivotal trials supporting products assessed by expedited pathways, surrogate endpoints reduce drug development time compared with waiting for the intended clinical outcomes. Whether surrogate endpoints supporting products authorised through CMA and AA pathways reliably predict clinical benefits of therapy has not been studied systematically. Our objectives were to determine the extent to which surrogate endpoints are used and to assess whether their validity had been confirmed according to published hierarchies.

METHODS AND FINDINGS

We used European Public Assessment Reports (EPARs) to identify the primary endpoints in the pivotal trials supporting products authorised through CMA or AA pathways during January 1, 2011 to December 31, 2018. We excluded products that were vaccines, topical, reversal, or bleeding prophylactic agents or withdrawn within the study time frame. Where pivotal trials reported surrogate endpoints, we conducted PubMed searches for evidence of validity for predicting clinical outcomes. We used 2 published hierarchies to assess validity level. Surrogates with randomised controlled trials supporting the surrogate-clinical outcome relationship were rated as 'validated'. Fifty-one products met the inclusion criteria; 26 underwent CMAs, and 25 underwent AAs. Overall, 26 products were for oncology indications, 10 for infections, 8 for genetic disorders, and 7 for other systems disorders. Five products (10%), all AAs, were authorised based on pivotal trials reporting clinical outcomes, and 46 (90%) were authorised based on surrogate endpoints. No studies were identified that validated the surrogate endpoints. Among a total of 49 products with surrogate endpoints reported, most were rated according to the published hierarchies as being 'reasonably likely' (n = 30; 61%) or of having 'biological plausibility' (n = 46; 94%) to predict clinical outcomes. EPARs did not consistently explain the nature of the pivotal trial endpoints supporting authorisations, whether surrogate endpoints were validated or not, or describe the endpoints to be reported in the confirmatory postmarketing studies. Our study has limitations: we may have overlooked relevant validation studies; the findings apply to 2 expedited pathways and may not be generalisable to products authorised through the standard assessment pathway.

CONCLUSIONS

The pivotal trial evidence supporting marketing authorisations for products granted CMA or AA was based dominantly on nonvalidated surrogate endpoints. EPARs and summary product characteristic documents, including patient information leaflets, need to state consistently the nature and limitations of endpoints in pivotal trials supporting expedited authorisations so that prescribers and patients appreciate shortcomings in the evidence about actual clinical benefit. For products supported by nonvalidated surrogate endpoints, postauthorisation measures to confirm clinical benefit need to be imposed by the regulator on the marketing authorisation holders.