# postMONARCH

Source: https://onco.cc/trials/postmonarch/  
OnCo record `postmonarch` (Trial). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Continuing CDK4/6 blockade with a different drug after the first one fails gives a small but real benefit.

## Summary

postMONARCH, trial NCT05169567 sponsored by Eli Lilly and reported in 2024, showed that continuing CDK4/6 blockade with a different drug after the first one fails gives a small but real benefit in HR-positive, HER2-negative advanced breast cancer. It randomised 368 women who had progressed on a CDK4/6 inhibitor plus endocrine therapy to abemaciclib or placebo with fulvestrant and met its primary progression-free survival endpoint, the first placebo-controlled phase 3 to show benefit from CDK4/6 inhibition beyond progression, with the largest gains in tumours without ESR1 or PIK3CA mutations. OnCo links it to CDK4/6 as a target, abemaciclib and fulvestrant. The absolute gain is modest, and whether biomarkers can pick the patients who benefit is the open question.

## Fields

- Kind: Trial
- Status: positive
- Last checked: 2026-09-07
- Registry id: NCT05169567
- Phase: 3
- Setting: HR+/HER2- advanced breast cancer after progression on CDK4/6 + endocrine therapy: abemaciclib + fulvestrant vs placebo + fulvestrant
- Sponsor: Eli Lilly
- Enrolled: 368
- Result: PFS 6.0 vs 5.3 months, HR 0.73.
- Outcomes: Progression-free survival: Abemaciclib + fulvestrant 6 months vs Placebo + fulvestrant 5.3 months, HR 0.73
- Replication: Contrasts with the negative PACE and PALMIRA trials of continuing palbociclib; MAINTAIN (ribociclib switch) was positive in phase 2.

## Sources

- ClinicalTrials.gov NCT05169567: https://clinicaltrials.gov/study/NCT05169567

## Connected records

- cancers: [HR-positive / HER2-negative breast cancer](https://onco.cc/cancers/breast-hr-positive/), [HR-positive metastatic breast cancer after CDK4/6 inhibitors](https://onco.cc/cancers/hr-positive-metastatic-post-cdk46/)
- technologies: [CDK4/6 inhibitors](https://onco.cc/technologies/cdk46-inhibitor/)
- targets: [CDK4/6](https://onco.cc/targets/cdk4-6/)
- drugs: [Abemaciclib](https://onco.cc/drugs/abemaciclib/), [Fulvestrant](https://onco.cc/drugs/fulvestrant/)
- companies: [Eli Lilly (incl. Loxo)](https://onco.cc/companies/eli-lilly/)
- roadmaps: [Hormonal therapy roadmap: removing the ovaries → tamoxifen → oral degraders switched by a blood test](https://onco.cc/roadmaps/hormonal-therapy-roadmap/)

---
JSON: https://onco.cc/api/v1/entities/postmonarch.json