trialsTrialPositive

postMONARCH

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

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.

Setting

HR+/HER2- advanced breast cancer after progression on CDK4/6 + endocrine therapy: abemaciclib + fulvestrant vs placebo + fulvestrant

Phase

Phase 3

Sponsor

Eli Lilly

Registry

Headline result

PFS 6.0 vs 5.3 months, HR 0.73.

Started

2022-03-11

Reported

2024

Enrolled

368 enrolled

Replication

Contrasts with the negative PACE and PALMIRA trials of continuing palbociclib; MAINTAIN (ribociclib switch) was positive in phase 2.

Outcomes

In plain words

What these results mean for people, not percentages

368 enrolled

Progression-free survivalprimarysurrogate endpoint

Median 6 vs 5.3 months with Abemaciclib + fulvestrant compared with Placebo + fulvestrant; about 0.7 months longer for half the group.
A median is a midpoint: half the people did better than this and half did worse, so it is not a prediction for any one person.
Put another way, the treated group had about 27 percent lower chance of the event at any given time (hazard ratio 0.73, likely range 0.57 to 0.95).

This is a surrogate endpoint: it measures the cancer being controlled or absent on scans and tests, which often, but not always, translates into living longer.
These results apply to the people the trial enrolled: HR+/HER2- advanced breast cancer after progression on CDK4/6 + endocrine therapy: abemaciclib + fulvestrant vs placebo + fulvestrant. People in a different situation may not see the same effect.
The trial selected people by a biomarker (HER2); the result should not be assumed for people whose cancer does not have it.

Numbers are from the trial as recorded here; see the source links in the table below. This is orientation, not medical advice: ask your team how closely the trial population matches you.

368 enrolled.

Progression-free survivalprimary

HR 0.73 (0.57 to 0.95) · p = 0.017

Download

Endpoint	Arm	n	Value	HR (95% CI)	p	Source
Progression-free survivalprimary	Abemaciclib + fulvestrant	182	6 months	0.73 (0.57 to 0.95)	0.017	link
Progression-free survivalprimary	Placebo + fulvestrant	186	5.3 months	0.73 (0.57 to 0.95)	0.017	link

Replication

Contrasts with the negative PACE and PALMIRA trials of continuing palbociclib; MAINTAIN (ribociclib switch) was positive in phase 2.

Connected

Similar pages

cancers

HR-positive / HER2-negative breast cancer HR-positive metastatic breast cancer after CDK4/6 inhibitors

technologies

CDK4/6 inhibitors

targets

drugs

ApprovedSmall-molecule CDK4/6 inhibitor

Abemaciclib · Verzenio

ApprovedInjectable SERD

Fulvestrant · Faslodex

companies

Eli Lilly (incl. Loxo)

roadmaps

Hormonal therapy roadmap: removing the ovaries → tamoxifen → oral degraders switched by a blood test