On September 11, 2025 Kazia Therapeutics Limited (NASDAQ: KZIA), an oncology-focused drug development company, reported new findings from a collaborative research program led by Professor Sudha Rao at QIMR Berghofer (Press release, Kazia Therapeutics, SEP 11, 2025, View Source [SID1234655934]).

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In this ex vivo study, blood samples from Stage IV HER2-positive metastatic breast cancer (mBC) patients were profiled to evaluate the effect of paxalisib, Kazia’s investigational PI3K–mTOR inhibitor, on metastatic burden. Paxalisib monotherapy demonstrated a statistically significant reduction in single circulating tumor cells and achieved a complete (100%) disruption of circulating tumor cell (CTC) clusters containing three or more cells."

Key Points
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HER2-positive breast cancer accounts for 15–20% of cases and remains a clinical challenge despite the transformative impact of HER2-targeted therapies, with many patients experiencing resistance, recurrence, or metastasis.

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Immunotherapy has demonstrated success across several solid tumors but has shown limited efficacy in HER2-positive breast cancer, underscoring the need for new therapeutic approaches.

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In this study, liquid biopsy profiling of Stage IV patients revealed that paxalisib treatment effectively disrupted CTCs and CTC clusters, which are considered biomarkers of aggressive disease and metastasis.

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Immunofluorescence analyses showed that paxalisib-treated blood samples from HER2-positive mBC patients achieved complete disruption of highly metastatic CTC clusters (≥3 cells).

"This monotherapy ex-vivo result extends our understanding of paxalisib’s potential beyond triple-negative breast cancer into HER2-positive disease," said Dr. John Friend, CEO of Kazia Therapeutics. "The ability to disrupt circulating tumor cell clusters, which are strongly associated with metastasis and poor prognosis, represents a transformative therapeutic avenue. We are particularly excited by the precision medicine aspect of this work, which leverages biomarkers to both track metastatic burden and guide therapeutic decisions. This work underscores Kazia’s commitment to expanding paxalisib’s utility across multiple subtypes of advanced breast cancer, addressing high unmet need in patients with limited options."

These findings complement Kazia’s ongoing Phase 1b trial in Stage IV triple-negative breast cancer (TNBC), where initial patient data announced in July 2025 demonstrated significant reductions in circulating tumor cells and clusters, underscoring the broader potential of paxalisib to address metastatic progression across multiple breast cancer subtypes.

Next Steps

Detailed datasets encompassing metastatic signatures and disrupted progenitor populations in Stage IV HER2-positive breast cancer have been submitted for presentation at an upcoming global oncology meeting in 2025.