Flare Therapeutics Reports Promising Phase 1A Results for First-in-Class PPARG Inhibitor FX-909 in Advanced Urothelial Cancer
Key Insights
Flare Therapeutics (search) presented updated Phase 1A data for FX-909, a first-in-class oral PPARG (search) inhibitor, showing tumor regression in 18 of 25 patients with PPARG-high advanced urothelial cancer (search).
The study demonstrated five confirmed partial responses and one complete response among biomarker-defined patients, with an acceptable safety profile across dose levels of 30-100 mg daily.
FX-909 is advancing to Phase 1B expansion targeting second-line treatment in biomarker-defined populations, with interim data expected in mid-2026.
Flare Therapeutics (search) presented encouraging Phase 1A clinical data for FX-909, a first-in-class oral small molecule inhibitor targeting peroxisome proliferator-activated receptor gamma (search) (PPARG (search)), at the 2026 ASCO Genitourinary Cancers Symposium. The data demonstrated meaningful antitumor activity in patients with advanced urothelial cancer (search) characterized by high PPARG expression.
Clinical Efficacy in Biomarker-Defined Population
As of the November 10, 2025 data cutoff, 46 patients with advanced urothelial cancer (search) received FX-909 monotherapy across four once-daily dose levels ranging from 30 mg to 100 mg. Patients had received a median of three prior lines of therapy, with 35% having received prior enfortumab vedotin and anti-PD(L)1 therapy.
Among efficacy-evaluable patients with PPARG (search)-high tumors, defined by a provisional tumor proportion score cutoff of ≥60%, 18 of 25 patients showed tumor regressions. This included five confirmed partial responses and one additional confirmed complete response in a patient with non-measurable disease.
"These data offer encouraging signs that FX-909 may help shrink or control tumors in patients with advanced UC, with enriched responses in tumors with a luminal lineage as defined by PPARG (search) overexpression," said Dr. Matthew Galsky, Professor of Medicine at the Icahn School of Medicine at Mount Sinai, who presented the data.
Durable Clinical Benefit Observed
Among the 25 patients in the PPARG (search)-high subgroup, five remained on treatment at the time of data cutoff, demonstrating sustained clinical benefit. Three patients at the 30 mg dose continued treatment for 5.3+, 5.8+ and 12.7+ months, one patient at 50 mg for 5.5+ months, and one patient at 70 mg for 7.6+ months. The patient with confirmed complete response remained on treatment for 8.4+ months.
Molecular biomarker analysis revealed that 80% (12/15) of the PPARG (search)-high subgroup achieved a circulating tumor DNA (ctDNA) complete response at cycle 2 or 3, with on-treatment declines in ctDNA associated with clinical benefit.
Safety Profile and Dosing Considerations
The safety analysis showed an acceptable tolerability profile across dose levels. At the 30 mg and 50 mg doses, the most common grade 3 treatment-related adverse events included anemia (18.9%), thrombocytopenia (16.2%) and fatigue (10.8%). Other frequent treatment-emergent adverse events included diarrhea (32.4%), hypertriglyceridemia (27%) and hyperglycemia (24.3%).
The 30 mg cohort demonstrated a more favorable safety profile with fewer grade 3 treatment-related adverse events (35.3%), longer time to onset (median 52 days), and reduced rates of dose interruptions (29.4%) and dose reductions (11.8%).
Addressing Significant Unmet Medical Need
Advanced urothelial cancer (search) represents an aggressive malignancy with limited treatment options and poor outcomes. The disease affects approximately 84,000 new cases annually in the United States, with urothelial carcinoma being the predominant histologic type. In advanced or metastatic stages, over 50% of patients experience disease progression within six to nine months of first-line chemotherapy, and the five-year survival rate remains below 6%.
Molecular subtyping has identified that luminal tumors characterized by high PPARG (search) expression comprise approximately 65% of advanced urothelial cancers. This translates to an estimated 14,000 new cases of advanced urothelial cancer (search) with high PPARG expression diagnosed annually in the United States. The PPARG pathway plays a critical role in maintaining tumor identity, promoting tumor growth, and contributing to immune evasion.
Next Steps in Clinical Development
FX-909 is currently being evaluated in a Phase 1B expansion study to determine the recommended Phase 2 dose in a biomarker-defined PPARG (search)-high patient population receiving second-line or later treatment. The study employs a randomized 2-stage design, with a validated immunohistochemistry-based test developed to identify eligible patients.
Flare Therapeutics (search) expects to report interim data from the randomized portion of the Phase 1B study in mid-2026. The company has developed FX-909 as part of its broader platform targeting transcription factors, a previously challenging target class in drug development.
"FX-909 is the first and only agent addressing the underlying transcriptional driver of urothelial cancer (search)," noted Dr. Galsky. "As an oral agent with an acceptable safety and tolerability profile, FX-909 has the potential to offer a much-needed new therapeutic option for patients with advanced UC, and over time, may extend into earlier lines of treatment."