Estimation of Percentage of Patients With Fibroblast Growth Factor Receptor Alterations Eligible for Off-label Use of Erdafitinib

Importance

When a novel drug is granted accelerated approval, both its on-label and off-label uses must be taken into account.

Objectives

To estimate the potential upper bound of off-label use of erdafitinib to treat advanced cancer with fibroblast growth factor receptor gene (FGFR) alterations, compare it to the upper bound of on-label use in urothelial cancer, and to review studies that may support off-label use.

Design, Setting, and Participants

This cross-sectional study used frequency data onFGFRalterations by cancer type and the estimated number of deaths from all cancers for 2019 in the United States. Mortality statistics were used as surrogates for patients with advanced cancer. Analysis was conducted in May 2019.

Exposure

Percentage of patients with anFGFR2orFGFR3alteration.

Main Outcomes and Measures

Estimated number of patients with advanced cancer expressing anFGFR2orFGFR3alteration eligible for off-label use of erdafitinib by cancer type; number of studies investigatingFGFR-targeting drugs for patients with cancer; and number of ongoing clinical trials on erdafitinib by cancer type.

Results

A total of 15 cancer types had reportedFGFRalterations. Of 455 440 estimated patients who died of cancer in 2019, 17 019 (3.7%) were estimated to haveFGFR2orFGFR3alterations. Of these patients, 12 955 (76.1%) could be eligible for off-label treatment with erdafitinib. A total of 29 completed studies evaluatedFGFR-targeting drugs in 11 cancer types, and 10 ongoing studies are studying erdafitinib for different oncological indications.

Conclusions and Relevance

This study indicates that the potential for off-label use ofFGFRinhibitors such as erdafitinib spans a number of cancer types and a large patient population. Systematic trials exploring off-label uses may be desirable for drugs that target clear, identifiable molecular alterations because this may be more efficient than off-label use in identifying clinical scenarios where the agent has activity.