Testing for ESR1 Mutations to Guide Therapy for HR-Positive, HER2-Negative Metastatic Breast Cancer Rapid Recommendation Update

Dr. Angie DeMichele and Dr. Lynn Henry present the latest rapid recommendation impacting two ASCO guidelines. This update focuses on testing for ESR1 mutations in patients with hormone receptor-positive, HER2-negative metastatic breast cancer, and presents treatment recommendations for patients with a detectable ESR1 mutation. Dr. DeMichele and Dr. Henry review the recent data from the EMERALD trial, discuss it's implications for practice, and ongoing developments they're monitoring for more effective therapeutic options. Read the latest update, "Testing for ESR1 Mutations to Guide Therapy for Hormone Receptor-Positive, HER2-Negative Metastatic Breast Cancer: ASCO Guideline Rapid Recommendation Update at www.asco.org/breast-cancer-guidelines. TRANSCRIPT This guideline, clinical tools, and resources are available at www.asco.org/breast-cancer-guidelines. Read the full text of the update and review authors’ disclosures of potential conflicts of interest disclosures in the Journal of Clinical Oncology, https://ascopubs.org/doi/10.1200/JCO.2300638  Brittany Harvey: Hello and welcome to the ASCO Guidelines Podcast, one of ASCO's podcasts delivering timely information to keep you up to date on the latest changes, challenges, and advances in oncology. You can find all the shows, including this one at asco.org/podcasts.  My name is Brittany Harvey, and today I'm interviewing Dr. Angie DeMichele from University of Pennsylvania, and Dr. Lynn Henry from the University of Michigan, authors on ‘Testing for ESR1 Mutations to Guide Therapy for Hormone Receptor-Positive, HER2-Negative Metastatic Breast Cancer: ASCO Guideline Rapid Recommendation Update’.  Thank you for being here, Dr. DeMichele and Dr. Henry. Dr. Angie DeMichele: It's a pleasure.  Dr. Lynn Henry: Thank you.  Brittany Harvey: Then, before we discuss this guideline, I'd like to note that ASCO takes great care in the development of its guidelines and ensuring that the ASCO conflict of interest policy is followed for each guideline. The disclosures of potential conflicts of interest for the guideline panel, including our guests on this podcast episode today, are available online with a publication of the rapid recommendation update in the Journal of Clinical Oncology, which is linked in the show notes.  So then, getting into the content of this rapid recommendation first, Dr. Henry, what prompted this rapid update, which provides updated recommendations for two ASCO guidelines? First, the ‘Biomarkers for Systemic Therapy and Metastatic Breast Cancer Guideline’, last published in 2022, and the ‘Endocrine Treatment and Targeted Therapy for Hormone Receptor-Positive, HER2-Negative Metastatic Breast Cancer Guideline’, which was last updated in 2021. Dr. Lynn Henry: Thank you, Brittany. There's been a lot of exciting news for the treatment of metastatic breast cancer in the last few years. This particular update reflects the results of the phase III EMERALD trial. This trial compared the new oral selective estrogen receptor degrader, elacestrant, to standard-of-care endocrine therapy with either fulvestrant or an aromatase inhibitor in patients with hormone receptor-positive, HER2-negative metastatic breast cancer that had previously progressed during treatment with a CDK4/6 inhibitor in combination with endocrine therapy. Compared to standard-of-care, in this trial, they showed improved progression-free survival in both the overall study population as well as specifically in the patients who had a detectable ESR1 mutation in their circulating tumor DNA. These findings were published in the Journal of Clinical Oncology in 2022, and the drug was subsequently approved by the US Food and Drug Administration in January 2023. Therefore, we felt that it was important to update the guidelines to reflect the results of this trial and the new drug approval.  Brittany Harvey: Excellent. Thank you for describing the results of that trial and the new approval.  So then, based on this data, Dr. DeMichele, what is the updated recommendation from the guideline expert panel for testing for ESR1 mutations?  Dr. Angie DeMichele: So, the guideline panel has now recommended that ESR1 mutation testing occur for any patient who develops a recurrence or progression on endocrine therapy. And this is specifically in reference to the development of ESR1 mutations that can occur after a patient has been exposed to aromatase inhibitors. The guideline itself recommends that this testing be done on either tumor or blood, but blood is preferable because there is increased sensitivity using ctDNA testing over tumor testing. So this was an important component of the change in the recommendation because it's linked to the approval of elacestrant as a therapy. Patients are only eligible to receive elacestrant if they harbor an ESR1 mutation. Brittany Harvey: Understood. I appreciate that explanation.   So then, Dr. Henry, following that recommendation for testing, what is the new recommendation for treatment for patients with a detectable ESR1 mutation? Dr. Lynn Henry: Yes. So patients who have a detectable ESR1 mutation and who have previously received treatment with endocrine therapy in combination with the CDK4/6 inhibitor for advanced breast cancer now have multiple treatment options. The newest option is this new drug, elacestrant, which is given 345 milligrams orally daily. There are still the other options that we already knew about, which include a different endocrine therapy alone, such as fulvestrant or an aromatase inhibitor, or possibly an endocrine therapy in combination with a targeted agent, such as alpelisib or everolimus. And those decisions really need to be based on what other mutations are present in the patient's cancer.  Importantly, at this time, there are no safety or efficacy data to support using elacestrant in combination with targeted agents. Therefore, to date, it has only been approved to be used as monotherapy. But really, this is an exciting new potential option for treatment for patients whose tumors have a detectable ESR1 mutation. Brittany Harvey: Yes, this is an exciting option, and I appreciate you describing how this fits in with the existing treatment paradigm for these patients.   So then, Dr. DeMichele, as these new recommendations are implemented, what should clinicians know? Dr. Angie DeMichele: I think this is a really important new step in breast cancer in testing for ESR1 mutations. We've not previously had a medication that required the existence of an ESR1 mutation for patients to be eligible for therapy. So obtaining ESR1 mutation testing may be new for some clinicians. As I stated earlier, this can be done either on a tumor biopsy or on blood testing using the Guardant360 ctDNA test, which is the test that was used in the clinical trial. And it was stated that the ctDNA test is more sensitive than the tumor test. But what's really important here is that the testing occur at the time that the clinician is considering switching therapies, because it's important to find that ESR1 mutation prior to starting the next therapy. ESR1 mutations don't typically exist in a tumor at the time it's diagnosed. They only emerge over time after patients have been exposed to different endocrine therapies, particularly aromatase inhibitors. It's also possible that at the time of a recurrence after aromatase inhibitor therapy or progression on an aromatase inhibitor, there will not be any detectable ESR1 mutation. However, with subsequent therapy, an ESR1 mutation can occur. So a patient may need serial testing over time to determine whether an ESR1 mutation has developed.  Brittany Harvey: Understood. Those are important clinical implications.  So then, Dr. Henry, Dr. DeMichele just described some of the testing implications for patients. But in your view, how does this rapid update impact patients with hormone receptor-positive, HER2-negative metastatic breast cancer? Dr. Lynn Henry: So as Dr. DeMichele mentioned, this update specifically highlights approval of a new drug, oral SERD elacestrant. This is an exciting new option for treatment of patients whose tumors have an ESR1 mutation. So previous data have demonstrated that cancers with ESR1 mutations do not respond as well to previously available standard-of-care treatments such as aromatase inhibitors. It's nice to have a drug that may be a better option than some of the previously existing treatments for hormone receptor-positive, HER2-negative metastatic breast cancer. Brittany Harvey: Definitely. That's great to hear.  So then, finally, Dr. DeMichele, are there ongoing research developments that the panel is monitoring for future updates to these guidelines? Dr. Angie DeMichele: We certainly are monitoring additional research developments, Brittany. Specifically, there are numerous other selective estrogen receptor degraders that are being tested, and these also may ultimately require ESR1 mutation testing and detection for therapies. So we'll be monitoring the results of those clinical trials. We'll also be watching for additional trials that help us understand how to best utilize elacestrant and whether it can be combined with other therapies. And then, finally, I think we have to think about how to place this in the context of other types of molecular changes that we may detect in metastatic breast cancer, such as PIK3CA mutations and others. And as we move forward, I anticipate that we will have additional therapies that are specifically targeted to molecular changes in the tumor. And I think this is a really exciting development because this is a major step forward toward precision medicine, where we're really tailoring the therapy to the specific biology of the patient's tumor and actually responding to the ways in which the tumor is evolving over time and in response to treatment. So as tumors become increasingly resistant to therapies, we can actually take advantage of those resistance mechanisms to develop therapies that will be more effective. Brittany Harvey: Yes, we'll look forward to those new therapies and research developments and then updated guidelines in the future.  So I want to thank you both so much for your work on this rapid recommendation update and for your time today, Dr. DeMichele and Dr. Henry.  Dr. Angie DeMichele: Thank you.  Dr. Lynn Henry: Thank you very much.  Brittany Harvey: And thank you to all of our listeners for tuning in to the ASCO Guidelines Podcast. To read the full guidelines, go to www.asco.org/breast-cancer-guidelines. 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