Brightline-1 trial

Background

Randomized phase 2/3 trial (NCT05218499) of the oral MDM2–p53 antagonist brigimadlin versus standard-of-care doxorubicin as first-line therapy for MDM2-amplified, locally advanced or metastatic, unresectable/progressive/recurrent dedifferentiated liposarcoma (DDLPS). Phase 3 portion N=310.

Results

Interventions and follow up: Arm A: brigimadlin 45 mg PO once every 3 weeks (n=148).
Arm B: doxorubicin 75 mg/m² IV once every 3 weeks (n=162).
Primary endpoint: PFS by blinded independent central review.
mFollow up: NR.
Results: PFS: median 8.4 vs 7.2 months, HR 0.79 (95% CI 0.60–1.06), P=.096 — primary endpoint not met.
ORR (confirmed): 22.3% vs 8.6%.
OS: NR.

Adverse events

Grade ≥3 (brigimadlin arm): neutropenia 36.7%, thrombocytopenia 27.9%
Tolerability: authors note brigimadlin safety was not more manageable than doxorubicin.

Conclusions

Brigimadlin showed antitumor activity with a higher response rate but did not improve PFS over doxorubicin in first-line MDM2-amplified DDLPS; the doxorubicin control arm performed better than anticipated. Translational analysis confirmed TP53-pathway activation but identified no predictive biomarker.

Key Limitations

Primary PFS endpoint not met; unexpectedly strong control-arm (doxorubicin) performance complicates interpretation; adaptive phase 2/3 design with interim dose selection; no predictive biomarker found; OS immature; brigimadlin cytopenias and GI toxicity not more manageable than anthracycline.

Clinical Context

Doxorubicin remains the first-line standard for advanced DDLPS. Brigimadlin (BI 907828) is an investigational oral MDM2–p53 antagonist, not approved. This negative phase 3 leaves doxorubicin as standard of care and keeps MDM2 inhibition experimental; no change to NCCN or ESMO first-line soft-tissue-sarcoma recommendations.

References