If you would have included the next couple of sentences in your King & Spalding reference it may not have fit your narrative very well.
Consistent with FDA’s prior guidance on the use of RWD to develop RWE for regulatory decision-making5, the External Controls Draft Guidance clarifies that multiple sources of patient-level data could potentially serve as the control arm data in an externally controlled clinical trial, including but not limited to data from other clinical trials, registries, natural history studies, electronic health records (“EHR”), and medical claims data. The External Controls Draft Guidance emphasizes that summary-level data will not suffice for use in an externally controlled trial. FDA observes that it has previously relied on external controls on a case-by-case basis in clinical trials where there is a single prospective arm of patients assigned to the investigational drug. The draft guidance thus provides the example of use of historical control data in a disease where the natural history is well-defined and the disease is known not to improve with available therapies.
IMO, I think GBM is a disease where the natural history is well-defined and the disease is known not to improve with available therapies.
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