- In a phase 2 trial of cabozantinib, a potent oral multireceptor tyrosine kinase inhibitor, bone metastases showed a partial response in 38% of patients with hormone receptor (HR)-positive breast cancer.
Why this matters
- Up to 75% of patients with metastatic breast cancer have bone metastases, and that percentage is even higher in the subgroup with HR+ cancers.
- This phase 2 trial of cabozantinib is promising enough to warrant progression to a phase 3 trial.
- Phase 2 trial (N=52) of cabozantinib with a starting dose of 100 mg, which was subsequently reduced to 60 mg/day for 12 weeks.
- Primary outcome: response on an isotope bone scan, measured by percentage change from baseline according to 4 categories:
- Complete response.
- Partial response (≥30% reduction).
- Stable disease (between
- Progressive disease (≥20% increase).
- Funding: Exelixis, Inc.
- 38.5% of 52 patients had partial response; 11.5% had stable disease.
- 36.5% of patients discontinued by 12 weeks because of early progression or unacceptable toxicity.
- Median PFS was 4.3 months.
- Median OS was 19.6 months.
- Most frequent grade 3 or 4 toxicities were:
- Hypertension (10%).
- Anorexia (6%).
- Diarrhea (6%).
- Fatigue (4%).
- Hypophosphatemia (4%).
- High rate of discontinuations.
- Small sample.
- Single-group, open-label design.