# monarchE: two years of abemaciclib after surgery in high-risk, hormone-receptor-positive early breast cancer

Source: https://onco.cc/key-papers/paper-monarche-jco-2020/  
OnCo record `paper-monarche-jco-2020` (Key paper). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Adding two years of the CDK4/6 inhibitor abemaciclib to standard hormone therapy after surgery cut the risk of the cancer coming back by a quarter in women with node-positive, high-risk disease.

## Summary

Open-label phase 3 trial of 5,637 patients with hormone-receptor-positive, HER2-negative early breast cancer at high risk of recurrence (four or more positive nodes, or one to three nodes with grade 3, tumour 5 cm or more, or high Ki-67), randomised to standard endocrine therapy with or without two years of abemaciclib. Primary endpoint was invasive disease-free survival (iDFS).

At the pre-planned interim analysis, iDFS was improved (HR 0.75; 2-year iDFS 92.2% vs 88.7%). The benefit widened with time: at five years iDFS was 83.6% vs 76.0%, a 7.6-point absolute difference (HR 0.68), well after abemaciclib had stopped. It was the first adjuvant CDK4/6 inhibitor to succeed after palbociclib failed in PALLAS and PENELOPE-B.

## Fields

- Kind: Key paper
- Last checked: 2026-09-08
- Journal: Journal of Clinical Oncology
- Year: 2020
- DOI: 10.1200/JCO.20.02514
- Authors: Johnston SRD, Harbeck N, Hegg R, et al.
- Findings: Invasive disease-free survival HR 0.75 (95% CI 0.60-0.93) at the interim analysis; 2-year iDFS 92.2% vs 88.7%.; Five-year update (2024): iDFS 83.6% vs 76.0% (HR 0.68) and distant relapse-free survival 86.0% vs 79.2%, with the curves continuing to separate after treatment ended.; Diarrhoea occurred in over 80% of abemaciclib patients (mostly grade 1-2) and roughly one in six discontinued because of adverse events.; Ki-67 of 20% or more identified a higher-risk group but did not predict a larger relative benefit, so the label was later broadened to all high-risk node-positive patients.; Overall survival data remain immature.
- What it means: Women with hormone-receptor-positive, HER2-negative breast cancer that has spread to lymph nodes and has other high-risk features can now be offered two years of abemaciclib alongside their hormone therapy, with a durable reduction in relapse. It does not apply to node-negative or low-risk disease, and the diarrhoea and cost are real trade-offs to discuss.
- Caveats: No overall survival benefit has yet been shown.; Open-label design with an endpoint (iDFS) that includes second primary cancers.; The contrast with the negative PALLAS trial (palbociclib) is not fully explained: differences in drug, dose intensity, or population selection are all possible.; Two years of a costly oral drug for a 7-8 point absolute gain raises access questions in many health systems.

## Sources

- PubMed search: monarchE JCO 2020: https://pubmed.ncbi.nlm.nih.gov/?term=monarchE+abemaciclib+adjuvant+Johnston+2020
- ClinicalTrials.gov NCT03155997: https://clinicaltrials.gov/study/NCT03155997

## Connected records

- cancers: [High-risk early HR-positive breast cancer](https://onco.cc/cancers/hr-positive-early-high-risk/), [HR-positive / HER2-negative breast cancer](https://onco.cc/cancers/breast-hr-positive/)
- technologies: [CDK4/6 inhibitors](https://onco.cc/technologies/cdk46-inhibitor/), [Endocrine therapy (SERMs, AIs, SERDs)](https://onco.cc/technologies/endocrine-therapy/)
- targets: [CDK4/6](https://onco.cc/targets/cdk4-6/), [Estrogen receptor (ERα)](https://onco.cc/targets/estrogen-receptor/)
- drugs: [Abemaciclib](https://onco.cc/drugs/abemaciclib/)
- companies: [Eli Lilly (incl. Loxo)](https://onco.cc/companies/eli-lilly/)
- terms: [Hazard ratio (HR)](https://onco.cc/terms/hazard-ratio/), [Neoadjuvant / adjuvant / perioperative](https://onco.cc/terms/neoadjuvant-adjuvant/)
- trials: [monarchE](https://onco.cc/trials/monarche/), [NATALEE](https://onco.cc/trials/natalee/)
- people: [Andrew Wardley](https://onco.cc/people/andrew-wardley/), [Javier Cortés](https://onco.cc/people/javier-cortes/), [Joohyuk Sohn](https://onco.cc/people/sohn-joohyuk/), [Miguel Martín](https://onco.cc/people/miguel-martin/), [Sara M. Tolaney](https://onco.cc/people/sara-tolaney/), [Stephen Johnston](https://onco.cc/people/stephen-johnston/), [Zhi-Ming Shao](https://onco.cc/people/shao-zhi-ming/)
- bottlenecks: [Dormant cells and minimal residual disease](https://onco.cc/bottlenecks/b-dormancy-mrd/), [Prices and value](https://onco.cc/bottlenecks/b-drug-pricing/), [Toxicity and quality of life are undervalued](https://onco.cc/bottlenecks/b-toxicity-qol/)
- journals: [Journal of Clinical Oncology](https://onco.cc/journals/jco/)

---
JSON: https://onco.cc/api/v1/entities/paper-monarche-jco-2020.json