Shares of Aprea Therapeutics Inc fell 19.7% Thursday following the release of preliminary data from the company's Phase 1 dose-escalation study evaluating APR-1051, a WEE1 inhibitor, in patients with advanced solid tumors.
The company reported the trial's first unconfirmed partial response in a patient enrolled in the ongoing ACESOT-1051 study. That response occurred in an endometrial cancer patient treated at the 150 mg dose level, and was characterized by an approximately 50% reduction in the target lesion and a greater than 90% drop in CA-125, a tumor marker commonly assessed in this cancer type.
In addition to that single partial response, Aprea disclosed that earlier cohorts demonstrated multiple patients achieving stable disease accompanied by measurable tumor reductions. Those findings included a roughly 5% tumor reduction in a head and neck cancer patient treated at the 70 mg dose and a 15% tumor reduction in a colon cancer patient treated at the 100 mg dose.
The company is continuing dose escalation and is currently enrolling patients in the 220 mg cohort as it works to establish the recommended Phase 2 dose. Aprea stated that these initial observations provide early proof-of-concept for single-agent activity by APR-1051 and noted a potential dose-response trend across the various dose cohorts, though the company framed the results as preliminary.
Aprea has indicated that it will provide further updates in the first half of 2026 and expects to complete dose escalation later in that year. The market response on Thursday reflected investor reaction to the early-stage dataset.
Context and next steps
The ACESOT-1051 trial remains in a dose-finding phase with patient enrollment ongoing at higher dose levels. Data released to date are preliminary and include the single unconfirmed partial response and several instances of stable disease with modest reductions in tumor size at lower doses. The company plans milestone updates and to finish dose escalation later in the year.
Market reaction
Following the announcement, Aprea's share price declined sharply, with a reported 19.7% drop on the trading session when the early data were disclosed.
This article presents the company statements and reported trial results without additional commentary.