A Phase 1 interventional study of BBI-940 and Fulvestrant in Breast Cancer, Metastatic Breast Cancer and Advanced Breast Cancer, sponsored by Boundless Bio, Inc.. Terminated at 8 sites in United States. Open to participants aged 18 Years and older. Per ClinicalTrials.gov, last updated 2026-08-19.
Sponsored by Boundless Bio, Inc. · Phase 1, Interventional, and Treatment
This is a first-in-human, open-label, Phase 1 study evaluating BBI-940, an investigational kinesin oral molecular degrader, administered as monotherapy or in combination with fulvestrant in adults with advanced or metastatic breast cancer.
The study consists of two parts: Part 1 (dose escalation) and Part 2 (dose expansion).
Part 1 is a dose-escalation phase designed to evaluate the safety and tolerability of BBI-940 and to determine the recommended dose for expansion (RDE). Participants may have estrogen receptor-positive, HER2-negative (ER+/HER2-) breast cancer or triple-negative breast cancer of the luminal androgen receptor subtype (TNBC-LAR).
Part 2 is a dose-expansion phase designed to further evaluate BBI-940 at the selected RDE in defined participant populations.
Part 2A evaluates BBI-940 in combination with fulvestrant, including multiple dose cohorts to evaluate the safety of the combination regimen and to determine the combination RDE in participants with ER+/HER2- breast cancer without an ESR1 mutation.
Part 2B evaluates BBI-940 monotherapy at the RDE in participants with ER+/HER2- breast cancer with FGFR1 amplification.
Part 2C evaluates BBI-940 monotherapy at the RDE in participants with TNBC-LAR.
Across all parts of the study, treatment is administered in repeated 28-day cycles, and participants undergo protocol-specified safety assessments.
12,544 studies on the registry are indexed under Breast Neoplasms; 2,892 are open to participants now.
This study's enrollment of 8 is below the median of 72 across 9,303 interventional studies indexed under Breast Neoplasms.
Browse Breast Neoplasms studies →Boundless Bio, Inc. is the lead sponsor of 3 studies on the registry; none are open to participants now.
Counted across the registry records on this site, refreshed daily.
Key Inclusion Criteria
Key Exclusion Criteria
Participants receive BBI-940 given alone in multiple sequential dose escalation cohorts. BBI-940 is given orally in repeated 28-day cycles.
Drug: BBI-940
Participants receive BBI-940 in combination with fulvestrant. BBI-940 is given orally in repeated 28-day cycles at one of multiple potential dose levels.
Drug: BBI-940 · Drug: Fulvestrant
Participants receive BBI-940 given alone at the recommended dose for expansion (RDE). BBI-940 is given orally in repeated 28-day cycles.
Drug: BBI-940
Participants receive BBI-940 given alone at the recommended dose for expansion (RDE). BBI-940 is given orally in repeated 28-day cycles.
Drug: BBI-940
Oral small molecule degrader targeting Kinesin.
Selective estrogen receptor degrader administered intramuscularly.
Rate of dose limiting toxicities (DLTs) in each BBI-940 monotherapy dose escalation cohort.
DLTs will be assessed during the first 28 days of study treatment (Cycle 1) to establish the maximum tolerated dose (MTD) and the recommended dose for expansion (RDE) of BBI-940 as monotherapy.
Time frame: First 28 days of study treatment (through end of Cycle 1).
Incidence of treatment emergent adverse events (TEAEs) in each dose group and overall as assessed by CTCAE version 5.0.
Incidence of treatment emergent adverse events (TEAEs) will be assessed by maximum severity and maximum causality.
Time frame: First dose of study treatment through 30 days after the last dose of study treatment.
Incidence of study treatment discontinuation and/or interruption by dose group and overall.
The incidence of study treatment discontinuation and/or interruption will be assessed.
Time frame: First dose of study treatment through 30 days after the last dose of study treatment.
Objective response rate (ORR) per RECIST Version 1.1 by dose group and overall.
Objective response rate (ORR) will be summarized by dose group and overall, based on the number of participants achieving a best response of partial response or complete response.
Time frame: From first dose of study treatment until disease progression per RECIST 1.1, death, withdrawal, loss to follow-up, or study completion; tumor assessments every 8 weeks (±7 days); assessed up to approximately 3 years.
Progression Free Survival (PFS) per RECIST Version 1.1 by dose group and overall.
Progression-free survival is defined as the time from first dose of study treatment to the first documented disease progression per RECIST Version 1.1 or death from any cause, whichever occurs first.
Time frame: From first dose of study treatment until first documented disease progression per RECIST 1.1 or death from any cause, whichever occurs first; tumor assessments every 8 weeks (±7 days); assessed up to approximately 3 years.
Time of maximum plasma concentration (Tmax) of BBI-940.
Time of maximum plasma concentration (Tmax) of BBI-940 will be determined.
Time frame: From 0 hours through up to 24 hours after BBI-940 dosing.
Maximum observed plasma concentration (Cmax) of BBI-940.
Maximum observed plasma concentration (Cmax) of BBI-940 will be determined.
Time frame: From 0 hours through up to 24 hours after BBI-940 dosing.
Minimum observed plasma concentration (Ctrough) of BBI-940.
Minimum observed plasma concentration (Ctrough) of BBI-940 will be determined.
Time frame: From 0 hours through up to 24 hours after BBI-940 dosing.
Area under the plasma concentration-time curve (AUC) of BBI-940.
Area under the plasma concentration-time curve (AUC) of BBI-940 will be determined.
Time frame: From 0 hours through up to 24 hours after BBI-940 dosing.
Plan to share: No
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This study is terminated, as verified in Feb 2026. You cannot join it, but the record below documents what was studied.
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Boundless Bio, Inc.