ER mutation

Among patients with ER-positive, HER2-negative advanced breast cancer, treatment with imlunestrant led to significantly longer progression-free survival than standard therapy among those with ESR1 mutations but not in the overall population. Imlunestrant-abemaciclib significantly improved progression-free survival as compared with imlunestrant, regardless of ESR1-mutation status. (Funded by Eli Lilly; EMBER-3 ClinicalTrials.gov number, NCT04975308.).

P3, N=240, Recruiting, MedSIR | Not yet recruiting --> Recruiting | Initiation date: Sep 2024 --> Dec 2024

While anti-estrogens that degrade ERα (fulvestrant) or block estrogen production (aromatase inhibitors) have improved patient outcomes, clinically important challenges remain related to drug administration, limited bioavailability, lack of brain exposure, and acquired resistance due to ESR1 mutations...Combining imlunestrant with abemaciclib (CDK4/6 inhibitor), alpelisib (PI3K inhibitor), or everolimus (mTOR inhibitor) further enhanced tumor growth inhibition, regardless of ESR1 mutational status. In an ER+ breast cancer intracranial tumor model, imlunestrant prolonged survival compared to vehicle or alternative SERD therapies. Together, these finding support the potential of imlunestrant to degrade ERα and suppress the growth of ESR1 wildtype and mutant breast cancer, including brain metastatic tumors.

P1, N=12, Recruiting, University of Wisconsin, Madison | Trial completion date: Dec 2025 --> Dec 2026 | Trial primary completion date: Dec 2024 --> Dec 2025

While some benefit, albeit modest, has been observed from switching to a different CDK4/6i after progression (e.g. ribociclib after palbociclib in the MAINTAIN trial and abemaciclib after both palbociclib and ribociclib in the postMONARCH trial), the current evidence (mainly with palbociclib) clearly argues against maintaining the same CDK4/6i. However, selected patients with indolent disease, prolonged exposure to previous CDK4/6i treatment (especially palbociclib) and without actionable molecular alterations, may be suitable for suchmaintenance strategy beyond progression. In this challenging and rapidly evolving treatment landscape, ongoing studies can refine the optimal approach and identify clinical and molecular factors to select the best treatment for the right patient.

YS mutant BC cells induced the conversion of fibroblasts into CAFs, via YAP, which represent a potential therapeutic target which interrupt the functional interactions between mutant cells/TME and to be implemented in the novel therapeutic strategy of a subset of metastatic BC patients carrying the frequent Y537S mutations.

We achieved a remarkable response in the metastatic lesions with minor toxicity issues. This case highlights the importance of utilizing up-to-date therapeutic agents and reactive decision-making during personalized cancer treatment.

The APIS ESR1 Mutations Kit demonstrated high sensitivity and specificity as a qualitative qPCR assay for detecting ESR1 mutations in varying WT backgrounds. Its performance with the SensID ESR1 Reference Set 1% AF cfDNA validated the kit's LoD at ≤1% MAF with external samples. The APIS kit is a valuable tool for assessing ESR1 mutations in both clinical and research settings, offering a more accessible alternative to traditional next-generation sequencing (NGS) and dPCR assays.

P3, N=400, Not yet recruiting, Fudan University Shanghai Cancer Center; Fudan University Shanghai Cancer Center

However, clinical trials have been predominantly carried out with selected populations and single drugs (Palbociclib, Ribociclib or Abemaciclib). At baseline, and considering the pre-defined criteria, ctDNA analysis detected PIK3CA mutations in 32.25% and 44.44% of patients by AVENIO and ddPCR, respectively. ESR1 mutations were detected in 3.22% and 9.37% by AVENIO and ddPCR, respectively. For PIK3CA mutations, the Kappa value was 0.62 (p-value: 0.0004) and 0.47 for ESR1 mutations (p-value: 0.0039).

In conclusion, employing enrichment techniques for low-allele frequency variants can improve the sensitivity of ESR1 mutation detection in breast cancer. This approach has the potential to enhance our ability to monitor and respond to disease progression dynamically, ultimately supporting more effective, individualized patient care.

PF-07248144 in combination with fulv demonstrated an acceptable safety profile and promising efficacy in pts with ER+ HER2− mBC post CDK4/6i and ET. Antitumor activity was observed irrespective of ESR1 and PIK3CA/AKT1/PTEN mutation status, endocrine sensitivity or resistance, duration of prior CDK4/6i treatment (12 mos), prior fulvestrant treatment, and 2L or later line therapy. These findings suggest that PF-07248144 in combination with ET may potentially overcome endocrine resistance and CDK4/6i resistance and provide a novel mechanism to address high unmet medical need in HR+ mBC after prior CDK4/6i and ET.

Median PFS after detection of ESR1 mutation was 3.2 months (range 1.9 –30.7), with all patients receiving HER2-directed therapy and four patients receiving Fulvestrant... Patients who develop ESR1 mutations in the setting of HER2+ mBC most often had point mutations in L536, E380 and D538, and had high rates of co-mutation with PIK3CA, which may have prognostic implications. To date, clinical trials regarding ESR1 mutations in breast cancer have excluded patients with HER2+ disease. These patients should be included in future studies of ESR1-targeted therapies.

Part 1 included treatment with fulvestrant (FUL) 500 mg + E7090 (105 or 140 mg) or exemestane (EXE) 25 mg + E7090 (105 or 140 mg). These results emphasize that FGFR pathway activation evaluated with mRNA expression of selected genes at BL—rather than FGFR gene abnormalities—is a key molecular determinant for sensitivity to E7090, an FGFR inhibitor. Future validation of these biomarkers is necessary in a larger population of people with ER+/HER2− BC.

A dilution series of DNA fragments, ranging from 5 to 10,000 copies per reaction, was analyzed to determine linearity. The kit's performance was further assessed using the SensID ESR1

In 1 pt, eribulin and abraxane did not have the same effect; ESR1 polyclonality was maintained. One pt with 1 ESR1 clone after 2.5 years of fulvestrant+palbociclib developed 15 additional clones after 1.5 years of an experimental SERD+everolimus. Another pt with 1 ESR1 clone after anastrozole+palbociclib developed 9 additional ESR1 clones after 10 months of AKT inhibition+anastrozole... This is the first investigation of dynamic changes in extreme ESR1 polyclonality in association with treatment outcomes in pts with ER+ MBC. Capecitabine was associated with a decrease in detectable ESR1-mutant clones, while increased polyclonality was found at progression on SERD+everolimus, AKT-inhibitor+AI, and an ADC. Although extreme ESR1 polyclonality is rare, understanding mutational dynamics will improve our understanding of polyclonality more broadly and its impact on treatment resistance.

TAKTIC was a phase Ib open-label trial evaluating ipatasertib in combination with fulvestrant, an aromatase inhibitor, or fulvestrant + palbociclib, in participants with HR+/HER2- MBC who received ≥1 line of prior therapy for MBC and had exposure to CDK4/6i (NCT03959891). Genomic insights using NGS suggest that MBC post-CDK4/6i is more susceptible to an AKTi-based treatment with ipatasertib in the presence of a PI3K/AKT/PTEN pathway mutation, whereas alterations in FGFR1 are associated with worse outcomes. This effort is one of very few studies prospectively evaluating mediators of AKTi response, an area of active interest given changes in the therapeutic landscape. The results presented here are hypothesis-generating; future work is underway to further expand upon these data.

Background Based on the positive results from the CAPItello-291 trial, capivasertib plus fulvestrant is a treatment option for adult patients with HR+/HER2− locally advanced or metastatic breast cancer who have progressed on an endocrine-based regimen and whose tumors harbor one or more alterations in PIK3CA, AKT1, or PTEN. Consistent with the literature, recurrent tissues were enriched for ESR1, BRCA2, GATA3, CDKN2A, and SMAD4 alterations, indicating a potential role for these gene alterations in driving disease recurrence. The PIK3CA/AKT1/PTEN-altered cohort was enriched for CDH1 mutations while the non-altered cohort was enriched for alterations in cell cycle-related genes previously associated with endocrine and cyclin-dependent kinase 4/6 inhibitor resistance.

None of the patients received ESR1-targeted therapy with Elacestrant. Our findings indicate that the level changes of ctDNA ESR1 mutations have implications with regards to treatment sensitivity and resistance to various therapies in patients with HR+/HER2- mBC. These results suggest a potentially effective method for monitoring treatment response and guiding future therapy by providing new insights into targeting ESR1 pathways to overcome resistance.

Elacestrant demonstrated a significant improvement in mPFS vs SOC in patients with both high and low ESR1 VAF. The clinical benefit and activity of elacestrant vs SOC was maintained regardless of type of ESR1 mutation variant and the abundance/quantity of ESR1 mutations in patients with ER+/HER2- mBC. In all patients with ER+/HER2, ESR1-mut mBC, elacestrant may replace fulvestrant-based combinations, and delay chemotherapy or ADC-based regimens.

Taken together, these data indicate that ESR1 mutations confer chemoresistance through activation of the JNK/MDR1 axis. These finding suggest a novel treatment option for BC tumors expressing ESR1 mutations.

Estrogen receptor one (ESR1) gene mutations, driving resistance to aromatase inhibitors (AIs), may guide the use of fulvestrant or emerging oral selective estrogen receptor degraders (SERDs) like elacestrant. Targeting mutations like breast cancer gene 1 and 2 (BRCA 1/2) with Poly (ADP-ribose) polymerase (PARP) inhibitors or the PI3K/AKT/mTOR pathway provides therapeutic options. The advent of antibody-drug conjugates (ADCs) like trastuzumab deruxtecan (T-DXd) and novel agents targeting Trophoblast cell surface antigen-2 (Trop-2) introduces further complexity, underscoring the need for early intervention targeting specific genomic alterations in metastatic BC.

In the liquid biopsies, we detected ESR1 mutations in 42 cases (25.9%) and ERBB2 mutations in six cases (3.7%), arguing for a change in therapy to fulvestrant, elacestrant, or neratinib. Furthermore, 17 cases had detectable TP53 mutations, associated with resistance against endocrine therapy. We conclude that liquid biopsy testing is a noninvasive, sensitive, and helpful method to optimize therapeutic decisions in metastatic BC.

The developed novel multi-marker liquid bead array assay for the simultaneous detection of PIK3CA and ESR1 hotspot mutations in single CTCs is highly specific, highly sensitive, high-throughput, and sample-, cost-, and time-saving. This multi-marker liquid bead array assay can be extended to detect up to 100 mutations in many genes at once and can be applied for bulk CTC and ctDNA analysis.

This review highlights recent efforts in drug development of next generation ER-targeted agents, including oral selective ER degraders (SERDs), proteolysis targeting chimera (PROTAC) ER degraders, other innovative molecules such as complete estrogen receptor antagonists (CERANs) and selective estrogen receptor covalent antagonists (SERCAs). The drug design, efficacy and clinical trials for each compound were detailed.

P3, N=312, Active, not recruiting, AstraZeneca | Recruiting --> Active, not recruiting

P=N/A, N=70, Recruiting, AstraZeneca | Trial completion date: Dec 2024 --> Dec 2025 | Trial primary completion date: Dec 2024 --> Dec 2025

Furthermore, we highlighted that the ER mutations could potentially predict clinical outcomes of immunotherapy. Our computational and clinical assessment underscore the utility of MERIN for elucidating the functional relevance of ER mutations in cancer immune response, potentially aiding patients' stratification for immunotherapy.

This analysis identified acquired gene alterations in patients with HR+/HER2- advanced breast cancer treated with ribociclib plus ET or placebo plus ET. These data may support further studies on acquired resistance mechanisms and inform future systemic interventions in the post-CDK4/6 inhibitor setting.

Oral SERDs constitute an exciting new drug class. Ongoing and future research will further refine the role of these drugs next to standard endocrine treatments and targeted therapies.

No such effect was observed for ESR1 mutations, with a rate ratio of 1.15 (confidence interval 0.67-1.95). We conclude that ER loss and ESR1 mutation together account for 30% of the resistance to endocrine therapy.

More recently, oral SERDs have been tested in patients with early hormone receptor positive breast cancer, although their impact on survival and in this curative setting compared to standard endocrine therapy still needs to be elucidated. The best timing and duration of SERD administration and specific biomarkers in (neo)adjuvant setting remain largely unknown.

Imlunestrant, as monotherapy or in combination with targeted therapy, had a manageable safety profile with evidence of preliminary antitumor activity in ER+/HER2- ABC.

Molecular profiling allowed the identification of ESR1Y537S, in an aggressive prolactinoma. ESR1Y537S was not detected early in the course of the disease and is likely conferring tumor aggressiveness. This finding emphasizes the significance of estrogen receptor signaling in prolactinomas. It also allowed the use of targeted therapy with successful control of disease progression.

P1/2, N=49, Active, not recruiting, Carrick Therapeutics Limited | Recruiting --> Active, not recruiting

The primary endpoint is distant metastasis free survival and secondary endpoints are invasive disease-free survival, relapse-free survival, overall survival, safety and quality of life. Recruitment started in December 2023 in Belgium and is planned to open in 11 more countries in 2024: Cyprus, France, Germany, Greece, Italy, Ireland, the Netherlands, Portugal, Spain, Sweden, and Switzerland.

The APIS ESR1 Mutations Kit showcased highly specific and sensitive detection of both the mutations present in the SensID ESR1 Reference Set 1% AF cfDNA and wildtype ESR1 from highly fragmented FFPE-derived DNA. Here, the kit’s LoD was affirmed at ≤1% MAF for cfDNA-based sample types and compatibility for detecting ESR1 mutations was demonstrated with both cfDNA and FFPEderived DNA samples.

P=N/A, N=70, Not yet recruiting, AstraZeneca

No abstract available

Camizestrant is a next-generation oral SERD and pure ER antagonist with a tolerable safety profile. The pharmacokinetics profile supports once-daily dosing, with evidence of pharmacodynamic and clinical efficacy in heavily pre-treated patients, regardless of ESR1m. This study established 75, 150 and 300 mg QD doses for Phase 2 testing (SERENA-2, NCT04214288 and SERENA-3, NCT04588298).

Elacestrant, a second-line ER degrader, increases overall free-survival in patients with resistant breast cancer and ESR1Y537S...Abstracts presented at a news conference are embargoed until the date and time of the news conference. The Endocrine Society reserves the right to lift the embargo on specific abstracts that are selected for promotion prior to or during ENDO.

P3, N=240, Not yet recruiting, MedSIR