When is one trial enough? How the FDA weighed the evidence in three programs

Q: When is one trial enough? How the FDA weighed the evidence in three programs

The three records frame the requirement in different terms. Replimune's single-arm trial drew two letters asking for adequate and well-controlled trials, then, by the company's account, accelerated approval on response rate and duration of response. Outlook reports that on appeal the Office of New Drugs counted NORSE TWO together with confirmatory evidence, including NORSE EIGHT, as substantial evidence. Aldeyra quotes its 2026 letter as finding that the totality of evidence from several trials did not support effectiveness.

What the evidence shows

Replimune: a single-arm trial. According to the FDA's April 2026 letter, the agency had said in 2021 that it would not recommend that the Sponsor submit a BLA based on the results of a single-arm study FDA · Apr 10, 2026 · p. 3. Replimune's 8-K describes the same minutes differently: if the data was sufficiently compelling, a single arm trial could be acceptable for consideration under accelerated approval 8-K · Apr 13, 2026. The FDA's first letter, in July 2025, said the trial was not designed to isolate the contribution of vusolimogene oderparepvec to the observed ORR when administered in combination with nivolumab FDA · Jul 21, 2025 · p. 1, and asked for more trials: you must conduct and provide the results from adequate and well-controlled clinical trial(s) which demonstrate substantial evidence of effectiveness FDA · Jul 21, 2025 · p. 2. The second letter repeated the request word for word: you must conduct and provide the results from adequate and well-controlled clinical trial(s) which demonstrate substantial evidence of effectiveness FDA · Apr 10, 2026 · p. 6.

Replimune's approval came through a different standard. Its August 2026 8-K reports that the indication is approved under accelerated approval based on objective response rate and duration of response 8-K · Aug 7, 2026, in 91 patients with at least one non-injected lesion included in the efficacy-evaluable population 8-K · Aug 7, 2026, and that Continued approval for this indication may be contingent on verification of clinical benefit in a confirmatory trial(s) 8-K · Aug 7, 2026. The FDA's approval letter is not in this record. How did RP1 go from a second FDA letter to accelerated approval in four months?

Outlook: one successful trial and a second that missed. After a 2023 letter, Outlook's 10-K says, we learned that the FDA required the completion of an additional adequate and well-controlled clinical trial 10-K · Dec 19, 2025. That trial, NORSE EIGHT, did not meet the pre-specified non-inferiority endpoint at week 8 8-K · Nov 27, 2024. As Outlook reports the August 2025 letter, because ONS-5010 did not meet the primary efficacy endpoint in NORSE EIGHT, it is recommended that confirmatory evidence of efficacy be submitted 8-K · Sep 2, 2025, and the FDA reiterated that NORSE TWO met its primary endpoint for effectiveness 8-K · Sep 2, 2025. The first page of each of the FDA's 2025 letters, which states the deficiency, has no text layer in the published PDF, so the letters' own words on it are not quotable here; this account is Outlook's.

The December 2025 letter, as Outlook reports it, found that the mechanistic and natural history data does not alter the previous review conclusion that while the one adequate and well-controlled study demonstrated efficacy 8-K · Jan 2, 2026, and that the FDA has not indicated what type of confirmatory evidence would be acceptable 8-K · Jan 2, 2026. On appeal, by Outlook's account, the Office of New Drugs determined that the results of the NORSE TWO trial, together with confirmatory evidence including NORSE EIGHT, natural history, and mechanistic and pharmacodynamic data, establish substantial evidence of effectiveness 8-K · May 26, 2026, and therefore additional trials are not required 8-K · Jun 1, 2026. The decision itself is not in this record. How did evidence the FDA said did not alter its conclusion come to establish substantial evidence?

Aldeyra: several trials. Its 10-K quotes the 2023 letter as asking that at least one additional adequate and well-controlled study to demonstrate a positive effect on the treatment of ocular symptoms of dry eye 10-K · Feb 27, 2026 be conducted. The April 2025 letter, on page 2, says the same: You should conduct at least one additional adequate and well controlled study to demonstrate a positive effect on the treatment of ocular symptoms of dry eye FDA · Apr 2, 2025 · p. 2, after finding the Study 030 primary efficacy endpoint analysis problematic FDA · Apr 2, 2025 · p. 2.

The March 2026 letter, as Aldeyra's 8-K quotes it, looked at the trials together: the inconsistency of study results raises serious concerns about the reliability and meaningfulness of the positive findings 8-K · Mar 17, 2026, and the totality of evidence from the completed clinical trials does not support the effectiveness of the product 8-K · Mar 17, 2026. Aldeyra reports that The FDA did not recommend conducting additional trials or request submission of additional confirmatory evidence 8-K · Mar 17, 2026, and counts nine adequate and well-controlled clinical trials, five of which achieved all multiplicity-controlled primary endpoints 8-K · Sep 29, 2026. Page 1 of each Aldeyra letter, where the finding is stated, is a scanned image with no text layer, so the 2026 finding is quoted here only as Aldeyra's 8-K quotes it. What changed between the FDA's 2025 and 2026 letters on reproxalap?

Set side by side, the three records frame the requirement differently. Replimune's letters ask for adequate and well-controlled trials; Outlook's, as the company reports them, for confirmatory evidence beside one successful trial; Aldeyra's 2026 letter, as the company quotes it, weighs the totality of evidence across trials. The phrase "substantial evidence of effectiveness" appears in all three records: in Replimune's letters, in Outlook's account of its appeal, and in Aldeyra's quotation of a lack of substantial evidence consisting of adequate and well-controlled investigations 8-K · Mar 17, 2026. Aldeyra's appeal is pending in this record, and the FDA's reasoning on Outlook's appeal is known here only through Outlook's filings.

Questions this raises

Comparing these records raises new questions. They are not yet investigated.

How did the FDA treat analyses that were not pre-specified in each of these programs?
What would each program's confirmatory trial have to show, according to its record?

The documents, by date

The passages quoted

Outlook Therapeutics Form 8-K, filed November 27, 2024

ONS-5010 did not meet the pre-specified non-inferiority endpoint at week 8 set forth in the special protocol assessment (SPA) with the U.S. Food and Drug Administration (FDA).