Kazia Therapeutics Ltd. (NASDAQ: KZIA) disclosed new data from its ongoing Phase 1b clinical study evaluating the safety and efficacy of paxalisib combined with pembrolizumab and chemotherapy in patients diagnosed with late-stage (Stage IV), metastatic triple-negative breast cancer (TNBC). Pembrolizumab is marketed by Merck & Co. Inc. (NYSE: MRK) under the Keytruda brand name.
This update arrives following Kazia Therapeutics' successful capital raise of approximately $46.5 million completed in December 2025, funds which are allocated to sustain the development of their lead compound, paxalisib, through advanced clinical studies.
Within the current trial, three metastatic TNBC patients treated with paxalisib-based regimens exhibited meaningful clinical responses. Notably, two patients achieved partial responses (PRs) within the formal trial setting, while one patient attained a confirmed complete metabolic response (CR) through an expanded access program.
Clinical Outcomes and Tolerability Profile
The two evaluable patients enrolled in the Phase 1b trial thus far both attained partial responses. Additionally, one individual with advanced metastatic TNBC recorded a confirmed complete metabolic response after a subsequent treatment cycle comprising pembrolizumab, chemotherapy, and paxalisib administered under expanded access protocols. These responses occurred in cases characterized by visceral involvement and disease affecting multiple organs.
Patients have remained on treatment for a median duration of approximately 6.1 months at the time of this update, with all subjects continuing therapy. Paxalisib, dosed at 30 mg daily alongside pembrolizumab and chemotherapy, maintained a generally favorable safety and tolerability profile. Among adverse events, a single occurrence of Grade 1 hyperglycemia was reported, which required no medical intervention.
Two serious adverse events (SAEs) have been documented during the trial, both assessed as unrelated to paxalisib administration.
Trial Expansion and Future Milestones
Looking ahead, Kazia Therapeutics anticipates activating two additional clinical trial sites by April 2026, with plans to add two more around mid-2026. The company remains on track to enroll a total of twelve TNBC patients in this study by the end of 2026, aiming for a topline data readout in early 2027.
Beyond metastatic TNBC, Kazia is exploring the utility of paxalisib in other breast cancer subtypes. Trials are underway or planned in earlier-stage TNBC populations as well as hormone receptor–positive, HER2-negative (HR+/HER2-) breast cancer cohorts, where dysregulation of the PI3K/mTOR pathway—a key signaling mechanism targeted by paxalisib—is well documented.
Presented data from July 2025 include a notable example of a 61-year-old woman patient with metastatic TNBC localized to the left upper lung lobe. Preliminary results at day 21 post-treatment revealed over a 50% reduction in circulating tumor cells (CTCs) and a significant decline in circulating tumor cell clusters, suggesting promising biological activity of the combination regimen.
Market Response
Following the clinical update, shares of Kazia Therapeutics initially surged to a high of $8.73 but retraced to close down by 10.21%, trading at approximately $7.12 at the last market check on Tuesday, reflecting a dynamic investor response to the evolving data.
Summary
Kazia Therapeutics is advancing its Phase 1b trial investigating paxalisib in combination with pembrolizumab and chemotherapy for patients with metastatic triple-negative breast cancer. Early clinical responses, including complete metabolic remission and partial responses in visceral and multi-organ metastatic disease, are encouraging. Safety data remain favorable with manageable adverse events. The company plans to expand enrollment and trial sites through 2026, targeting additional breast cancer indications influenced by PI3K/mTOR pathway dysregulation. Topline results are expected in early 2027, which will be critical in assessing paxalisib’s clinical potential in these indications.