Oral SERDs for ER-Positive, HER2-Negative Advanced Breast Cancer: FDA and EMA Approvals, Efficacy and Safety

Oral SERDs for ER-positive, HER2-negative advanced breast cancer: FDA and EMA approvals, efficacy and safety

Three oral selective estrogen receptor degraders (SERDs) now hold both FDA and EU authorisations for ER-positive, HER2-negative advanced breast cancer: elacestrant (Orserdu), imlunestrant (Inluriyo) and camizestrant (Etcamah). All three are restricted to tumours with an ESR1 mutation. They split into two regulatory models:

• Monotherapy after endocrine progression. Elacestrant and imlunestrant were approved on PFS benefit confined to the ESR1-mutated subgroup. Neither showed benefit in patients without a detected mutation.
• ctDNA-guided switch with a CDK4/6 inhibitor. Camizestrant is authorised in combination with a CDK4/6 inhibitor. Treatment switches when an ESR1 mutation is detected during first-line aromatase inhibitor (AI) plus CDK4/6 inhibitor therapy, before disease progression.

Imlunestrant plus abemaciclib is where the agencies split. FDA added the combination to the US label in 2026. In the EU, the applicant withdrew the combination indication after CHMP raised major concerns about trial design.

Approval landscape

Recommended doses (all once daily, oral).

• Elacestrant: 345 mg with food ²⁴⁶. The EU allows dose reduction to 258 mg ³⁵⁴.
• Imlunestrant: 400 mg on an empty stomach ⁶¹.
• Camizestrant: 75 mg with or without food, together with the CDK4/6 inhibitor at the dose the patient was already taking ³⁷⁴.

Wording differences between agencies.

• EMA labelling calls elacestrant ³⁵⁶ and camizestrant ¹⁵² SERDs.
• The FDA labels for Orserdu and Etcamah use "estrogen receptor antagonist" wording, while describing ERα degradation for camizestrant ²⁴⁵³⁷⁶.
• FDA materials explicitly call imlunestrant a SERD ⁵⁴.
• Both EU indications for imlunestrant and camizestrant require an LHRH agonist (camizestrant also allows an antagonist) for pre- or perimenopausal women and for men ¹¹⁵¹³⁷.

A note on class boundaries. FDA also approved vepdegestrant (Veppanu, NDA 219835) on 1 May 2026 for ESR1-mutated ER-positive, HER2-negative advanced breast cancer after endocrine therapy ⁹¹²⁴. However, FDA gave it the established pharmacologic class "heterobifunctional protein degrader" (a PROTAC recruiting cereblon) and expressly distinguished it from SERDs ³⁴¹²³. No EU authorisation was identified. For that reason it is discussed here only for context.

Elacestrant (Orserdu)

Efficacy

EMERALD randomised 478 patients to elacestrant or standard-of-care endocrine monotherapy (investigator's choice of fulvestrant or an AI). PFS by blinded central review was the primary endpoint in both the overall population and the ESR1-mutated population (n=228) ²¹⁸²³⁰.

FDA view of the overall-population result. FDA concluded that the ITT result was driven by the 48% of patients with ESR1 mutations. It found no clinically meaningful benefit in the mutation-not-detected subgroup, especially given the added gastrointestinal toxicity ²³².

Overall survival. OS in the ESR1-mutated population was not statistically significant. The label reports HR 0.90 (95% CI 0.63 to 1.30) ²¹⁸. The EPAR reports median OS of 24.18 versus 23.49 months ²⁹¹.

Efficacy after prior CDK4/6 inhibitor therapy. All ESR1-mutated patients in EMERALD had received a CDK4/6 inhibitor before enrolment ²³⁰. The EPAR reports an exploratory trend: benefit was larger with longer prior CDK4/6 inhibitor exposure. With at least 12 months of prior exposure, median PFS was 8.61 versus 1.91 months (HR 0.41) ¹⁸². Even so, the EPAR states that the effect of prior CDK4/6 inhibition on elacestrant activity cannot be determined from the submitted data ¹⁸⁶¹⁹².

Combination data. No clinical data support combining elacestrant with a CDK4/6 inhibitor. The only combination evidence is a preclinical palbociclib xenograft study ¹⁸⁵.

Assessment issue flagged in the EPAR. Investigators and central review disagreed on progression. Investigators called progression earlier than central review in 32.6% of elacestrant patients versus 22.7% of SOC patients ²⁹². Sensitivity analyses remained supportive ²⁹⁷.

Safety

Grade 3 to 4 treatment-emergent adverse events (TEAEs) occurred in 27.0% of patients (treatment-related: 7.2%) ²⁷⁹. Other key findings:

• Common adverse reactions: musculoskeletal pain (41%), nausea (35%), fatigue (26%) and vomiting (19%) ²⁶⁸.
• Gastrointestinal excess versus SOC: nausea 35% vs 19%, vomiting 19% vs 9% ²⁸⁴.
• Serious and fatal adverse reactions: serious in 12%; fatal in 1.7%, none considered treatment-related ²⁶⁸²⁷⁹.
• Treatment modifications: permanent discontinuation 6%, dose interruption 15%, dose reduction 3% ²⁶⁸.
• FDA warnings and precautions: dyslipidemia (hypercholesterolemia 30%, hypertriglyceridemia 27%) and embryo-fetal toxicity ²⁷¹²⁷⁵.
• EU risk management: the RMP listed no important identified or potential risks. CHMP highlighted gastrointestinal events, hepatic impairment, CYP3A4 interactions and venous thromboembolism as precautions ³²⁵³³².

Imlunestrant (Inluriyo)

Monotherapy efficacy

EMBER-3 was an open-label phase 3 trial with three arms randomised 1:1:1:

• imlunestrant monotherapy
• investigator's-choice fulvestrant or exemestane
• imlunestrant plus abemaciclib ⁵²¹⁰³

Patients had progressed on an AI, with or without a CDK4/6 inhibitor. PFS in the ITT and ESR1-mutated populations were dual primary endpoints ⁶²⁸⁶.

Supporting analyses. Blinded central review in the ESR1-mutated population gave HR 0.657 ³²⁰.

Overall survival. OS was immature and not statistically significant. FDA found no evidence of OS detriment and required a postmarketing commitment for further OS analyses ⁵¹⁵⁰. Formal OS testing in the ITT population was not possible because the ITT PFS endpoint failed ³¹⁷.

CHMP criticisms of the trial. CHMP noted three limitations:

• ESR1 status was not a randomisation stratification factor ¹⁰³.
• The enrolled population was fitter than patients seen in routine practice ¹⁰³.
• 32 patients were inadvertently enrolled in the ESR1-mutated population. Excluding them gave HR 0.541 ³¹⁶.

Monotherapy safety

Grade 3 or higher TEAEs occurred in 17.1% of patients, versus 20.7% with SOC ³⁴¹⁷⁶. Other key findings:

• Common adverse reactions: musculoskeletal pain (30%), fatigue (23%), diarrhoea (22%) and nausea (17%) ³³⁴.
• Excess versus control: gastrointestinal events and fatigue were more frequent (diarrhoea 22% vs 12%, fatigue 23% vs 14%) ⁵⁹.
• Serious and fatal adverse reactions: serious in 10%; fatal in 1.8% ³³⁵.
• Treatment modifications: discontinuation 4.6%, dose reduction 2.4% ³³⁵.
• US label: the only warning and precaution is embryo-fetal toxicity ³³⁵.

EU-specific safety conclusions. CHMP classified venous thromboembolism as a common adverse drug reaction ⁷⁹⁸⁴. Three deaths from gastrointestinal bleeding were treated as a novel signal. Gastrointestinal bleeding was therefore added to the RMP as an important potential risk and a PSUR safety concern ⁷⁹.

Imlunestrant plus abemaciclib: divergent FDA and EMA outcomes

Original FDA review. FDA's 2025 review did not assess the combination arm. The proposed indication was monotherapy, so the combination was outside the NDA's scope ³⁰³³⁰⁵.

2026 US labelling update. The label now includes Inluriyo with abemaciclib for adults with ESR1-mutated ER-positive, HER2-negative advanced breast cancer after at least one line of endocrine therapy ³⁷¹. The supporting efficacy analysis was exploratory. In the ESR1-mutated population (n=159), median PFS was 11.1 months with the combination versus 5.5 months with imlunestrant alone (HR 0.53, 95% CI 0.35 to 0.80) ³⁷⁰⁹⁶.

Combination safety in the US label (n=208).

• Common clinical adverse reactions: diarrhoea 86% (grade 3 to 4: 9%), nausea 51% and fatigue 41% ³³⁸.
• Serious and fatal adverse reactions: serious in 21%; fatal in 3.8% ³³⁸.
• Treatment modifications: dose interruption 50%, dose reduction 18% ³³⁸.
• Laboratory abnormalities: neutrophil decrease in 86% (grade 3 to 4: 21%) ³¹¹.

EU outcome. The applicant withdrew the combination indication during assessment ¹¹³¹⁹⁹. Across the concurrently randomised ITT population, the combination improved investigator-assessed PFS over imlunestrant alone: 9.36 versus 5.49 months (HR 0.569) ³⁶⁶³⁶⁸. In CDK4/6 inhibitor-pretreated patients the difference was 9.1 versus 3.7 months ³⁶⁷. CHMP nonetheless raised the following concerns:

• Wrong primary comparison. Imlunestrant monotherapy had not beaten SOC in the ITT population, and the combination was compared with SOC only in exploratory analyses ³⁶⁶.
• Contribution of components not shown. The design could not isolate imlunestrant's added benefit on top of abemaciclib ³⁶⁶.
• Wrong comparator for CDK4/6 inhibitor-naive patients. Median PFS was identical in both arms (11.1 months), and the trial did not compare the combination with abemaciclib plus fulvestrant ³⁶⁷.
• Assessment bias. Open-label, investigator-assessed PFS carried a risk of ascertainment bias ³⁶⁷.
• Missing supporting data. No CDK4/6 inhibitor rechallenge data and no combination dose-finding were submitted ¹⁹⁹³⁶⁷.
• Immature OS. OS was not significant (HR 0.824, p=0.262) ³⁶⁶³⁶⁸.
• Tolerability. Dose interruptions or reductions were substantially more frequent with the combination ⁷⁵.

Camizestrant (Etcamah)

Efficacy with CDK4/6 inhibitors

SERENA-6 design. SERENA-6 was a double-blind trial that randomised 315 patients 1:1 ¹³⁵. All patients had a plasma ctDNA ESR1 mutation detected after at least 6 months of first-line AI plus CDK4/6 inhibitor therapy without progression. The arms were:

• switch to camizestrant, keeping the same CDK4/6 inhibitor
• continue the AI plus CDK4/6 inhibitor

The CDK4/6 inhibitors in use were palbociclib (75.6%), ribociclib (14.9%) and abemaciclib (9.5%). The primary endpoint was investigator-assessed PFS ¹³⁵.

PFS results.

• EPAR: 16.76 versus 9.23 months (HR 0.45, 95% CI 0.34 to 0.59; p<0.00001) ¹⁹⁸.
• US label: 16.0 versus 9.2 months (HR 0.44, 95% CI 0.31 to 0.60) ³⁶³.

Overall survival. OS was immature. The EPAR reports HR 0.87 (95% CI 0.57 to 1.30) at 30% maturity ¹⁹⁸. The FDA label reports 12% maturity at the PFS analysis ³⁶³. Final OS is an EU post-authorisation obligation due by 31 December 2028 ¹³⁹.

US approval terms. FDA granted accelerated approval based on PFS measured from ESR1 mutation detection ³⁷⁴³⁷⁷. The label specifies:

• ctDNA testing every 3 months until a mutation is detected ³⁷⁴
• a plasma ESR1 mutation detected with an FDA-authorised test ³⁷⁴

Retrieved materials do not address the switch strategy itself. Neither the retrieved FDA review nor the retrieved EPAR text discusses whether switching early on ctDNA detection is better than switching at progression, or how PFS2 findings were interpreted ³⁶³¹⁵⁰. These are the central open questions for this indication.

Safety

Safety data come from the pooled EU dataset of camizestrant plus a CDK4/6 inhibitor (n=263) and from SERENA-6 in the US label (n=155).

• Most common adverse reactions (EU): neutropenia 59.7% (grade 3 to 4: 46.4%), visual effects 40.7%, infections 38.4% and bradycardia 19.8% ¹⁴⁶.
• US label: visual disturbances in 34% (photopsia, blurred vision and related terms) and bradycardia in 8%. Mean heart-rate decrease was about 13 bpm, with the maximum at Day 15 ³⁷⁹³⁸⁰.
• Serious and fatal adverse reactions (US): serious in 10%; fatal in 1.3% ³⁷⁹³⁸⁰.
• Treatment modifications (US): camizestrant discontinuation 1.3%, dose interruption 22% ³⁷⁹.
• US boxed warning and warnings and precautions: Boxed warning for arrhythmia risk (Torsades de Pointes, other ventricular arrhythmias, and sudden death) when used with QTc-prolonging drugs such as ribociclib. Section 5 warnings and precautions are QTc interval prolongation, bradycardia, and embryo-fetal toxicity. Visual disturbances are adverse reactions with dose-modification guidance, not a numbered warning and precaution ^377378380.
• Exposure-response: higher camizestrant exposure was associated with more bradycardia and visual disturbance ³⁷⁶.
• EU assessment: EMA regarded bradycardia and visual disturbances as camizestrant-specific effects that warnings and monitoring can manage. Most serious events were attributed to known CDK4/6 inhibitor effects ¹⁴⁹. The EPAR also reports QTc prolongation in 6.8%, including one grade 4 non-fatal Torsades de Pointes event with ribociclib ¹⁴⁵¹⁵².

Cross-product observations for regulatory strategy

• ESR1 restriction is consistent across products and agencies. In every pivotal monotherapy trial, the ESR1-not-detected subgroup had HRs near or above 1 ^21786316. The EU restriction for imlunestrant was explicitly tied to this differential efficacy ³¹⁴.
• Companion diagnostics. US labels require an FDA-authorised plasma test ^24661374. EU labels allow a CE-marked IVD or another validated test if no IVD is available ³⁵⁴¹¹⁵.
• Monotherapy PFS gains were modest. Median PFS improvements in the ESR1-mutated population were about 1.6 to 1.9 months ¹⁹²³¹⁷. OS was immature or not significant at approval for every product. FDA required postmarketing OS analyses for imlunestrant ⁵⁰, and the EU imposed a post-authorisation OS obligation for camizestrant ¹³⁹.
• Safety profiles differ by agent.
  • Elacestrant: gastrointestinal toxicity and dyslipidemia ²⁸⁴²⁷¹.
  • Imlunestrant: gastrointestinal toxicity and fatigue, with venous thromboembolism and gastrointestinal bleeding flagged in the EU ⁵⁹⁷⁹.
  • Camizestrant: bradycardia, visual disturbances and QTc effects on top of the CDK4/6 inhibitor's cytopenias ¹⁴⁶³⁸⁰.
• Combination evidence is judged differently. FDA accepted exploratory ESR1-mutated PFS data for imlunestrant plus abemaciclib ³⁷⁰⁹⁶. CHMP required the combination to be compared against SOC, the contribution of each component to be shown, and dose-finding data ³⁶⁶¹⁹⁹. SERENA-6 met both agencies' expectations because it used a double-blind active control against the same CDK4/6 inhibitor backbone ¹³⁵.

Open questions

Several points could not be answered from the retrieved review text and would support deeper follow-up:

• FDA's reasoning on the ctDNA-guided switch paradigm for camizestrant, including PFS2 and patient-reported outcomes.
• The exact approval action and date for the US imlunestrant plus abemaciclib supplement.
• Reconciliation of the differing OS hazard ratios reported across FDA review documents for elacestrant and imlunestrant ^2222188651.