The 500 mg and 400 mg versions showed dose-limiting toxicities, the company statement said.
Shares of the Lexington, Mass., company at last check dropped 37% to $8.
The updated data from the study "further support the growing body of evidence that CA-4948's anti-cancer activity continues to deepen the longer patients remain on drug, which is enabled by its safety and durability profile to date," Chief Executive James Dentzer said in a statement.
"Further, after backfilling patient cohorts and evaluating additional data after the April 30, 2021, cutoff date for today's presentation, we have concluded 300mg BID is the optimal dose to take into Phase 2 studies."
Curis presented at the European Hematology Association 2021 Virtual Congress.
The reported data are from Curis's Phase 1/2 dose-escalation study for orally administered CA-4948, a monotherapy for adult patients with acute myeloid leukemia.
The primary endpoint of the study is to determine the maximum tolerated dose and recommended Phase 2 dose based on safety and tolerability.