SABCS 2022 | ELAINE 1: ESR1 mutations in ctDNA from ER+/HER2- mBC treated with lasofoxifene or fulvestrant

So at San Antonio 2022, there is a poster presentation looking at a subset analysis of blood and genomic analysis from the ELAINE 1 study. ELAINE is a look at lasofoxifene compared to fulvestrant in patients with hormone receptor-positive metastatic breast cancer. And this translational analysis is looking at the genomic clearance of ESR1 mutations. Now, we all understand that having an ESR1 mutation portends a slightly worse prognosis and that there are different ESR1 mutations. And so, importantly, in this analysis we saw that patients treated with lasofoxifene very effectively were able to clear ESR1 mutations. Specifically, in this study that accrued about 103 patients, we saw that there was an 83% rate of mutant ESR1 clearance in the patients that were treated with lasofoxifene, which was significantly better than those treated with fulvestrant.

Specifically, looking at patients with the Y537S alteration, which is maybe the worst of the ESR1 mutations. We also saw a significant outcome in terms of clearance of ESR1 mutation with 87% of patients treated lasofoxifene able to clear compared to only 61% of patients treated with fulvestrant able to clear the high-risk ESR1 mutation. And I think that this is really important as we consider how to move oral SERDs forward, particularly as we’re also exploring the role of CDK4/6 beyond, CDK4/6 inhibitor. If ESR1 mutations are potentially a predictor of a need to change the endocrine therapy backbone and to continue the CDK4/6 inhibitor, for example, this may be a predictor that a medicine lasofoxifene could play an important role in the treatment landscape.