Elacestrant Improves PFS In ER-Positive, HER2-Negative Metastatic Breast Cancer

Author: By Hannah Kitt, medwireNews Reporter 

medwireNews: Patients with oestrogen receptor (ER)-positive, HER2-negative, metastatic breast cancer who have progressed on prior therapies derive a significant progression-free survival (PFS) benefit from treatment with elacestrant versus other endocrine agents, suggest EMERALD results. 

“Elacestrant (RAD1901) is an oral SERD [selective oestrogen receptor degrader] that blocks ER and inhibits estradiol-dependent gene transcription induction and cell proliferation in ER+ [breast cancer] cell lines”, explained presenting author Aditya Bardia, from Massachusetts General Hospital Cancer Center in Boston, USA, at the 2021 San Antonio Breast Cancer Symposium in Texas, USA. 

He added that elacestrant has shown promising activity in postmenopausal women with ER-positive, HER2-negative, metastatic disease in a phase I study. 

Bardia now reported on the phase 3 trial, which included 477 men or postmenopausal women who had progressed on one or two lines of endocrine therapy for advanced disease, of which one was given in combination with a CDK4/6 inhibitor. Patients were allowed to receive one prior line of chemotherapy and the majority (69%) had visceral metastases. 

Treatment with elacestrant 400 mg/day significantly improved the co-primary endpoint of PFS by independent review in the intention-to-treat population, at a median of 2.79 months versus 1.91 months with investigators’ choice of single-agent endocrine therapy, most commonly fulvestrant (70%). This translated to a significant 30% reduced risk for progression or death in favour of the oral SERD.  

Noting that acquired ESR1 mutations often underlie resistance to first-line therapy in this population, Bardia shared data on the other primary endpoint, namely PFS among the 228 patients with mutant ESR1. In these patients, the risk for progression or death was a significant 45% lower in the elacestrant than the control group, and the respective median PFS durations were 3.78 and 1.87 months. 

The PFS rate was higher with elacestrant than other endocrine therapies at both 6 and 12 months, with corresponding rates of 34.3% versus 20.4% and 22.3% versus 9.4% in the intent-to-treat population and 40.8% versus 19.1% and 26.8% versus 8.2% in the ESR1-mutant population.  

The fact that elacestrant has clinical activity in patients who have received prior fulvestrant highlights that upon disease progression of first-line endocrine therapy, these tumours are still endocrine-sensitive, which points to “the need for better endocrine therapies,” said Aditya Bardia. He commented that “elacestrant is a great start,” but “there are other oral SERDs in development as well.” 

Aditya Bardia also reported results from the prespecified interim overall survival (OS) analysis, which he said “demonstrated a trend in favour of elacestrant.” He added that “the final [OS] analysis with mature data is expected to take place in late 2022/early 2023.” 

Presenting data on the safety profile, Aditya Bardia said that “[e]lacestrant was well tolerated with a predictable and manageable safety profile consistent with other endocrine therapies.” A total of 7.2% of elacestrant-treated patients experienced grade 3 to 4 treatment-related adverse events (TRAEs), as did 3.1% of those given the control regimen. The proportion of patients who needed a dose reduction due to any TRAE was 2.5% and 0.0%, respectively, while the corresponding rates of discontinuation were 3.4% and 0.9%. There were no treatment-related deaths in either of the groups.  

He concluded: “Clinically, elacestrant has the potential to become [a] new treatment option in the studied patient population.” 

Discussant David Cescon, from the Princess Margaret Cancer Centre in Toronto, Ontario, Canada, noted that the magnitude of clinical benefit from elacestrant is larger in those with versus without ESR1 mutations, and added: “While we do not have data for those patients who have ESR1 wildtype disease [we can infer that the benefit in this group] must be smaller, and may be quite small.” 

Reference  

Bardia A, Neven P, Streich G, et al. Elacestrant, an oral selective estrogen receptor degrader (SERD), vs investigator’s choice of endocrine monotherapy for ER+/HER2- advanced/metastatic breast cancer (mBC) following progression on prior endocrine and CDK4/6 inhibitor therapy: Results of EMERALD phase 3 trial. Abstract GS2-02; 2021 San Antonio Breast Cancer Symposium; Texas, USA: 7–10 December.