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A real-world study finds ESR1 mutations signal worse outcomes in metastatic breast cancer. Patients with ESR1-mutated HR+/HER2– metastatic breast cancer had a median progression-free survival of just 6.1 months, compared to 11.0 months for those without the mutation. When ESR1 mutations co-occurred with other genomic alterations, outcomes were even poorer — pointing to a high-risk subgroup that may need more targeted treatment strategies.
A retrospective, real-world study out of Rome is shedding new light on how ESR1 mutations — detected via circulating tumor DNA (ctDNA) — affect outcomes in patients with hormone receptor (HR)-positive, HER2-negative metastatic breast cancer. The single-center analysis of 72 patients found that those harboring ESR1 mutations fared significantly worse, with a median progression-free survival (PFS) of 6.1 months versus 11.0 months for patients with ESR1 wild-type disease.
The findings became even more notable when researchers looked at patients with ESR1 mutations plus additional genomic alterations. That subgroup (13 patients) had a median PFS of just 7.0 months, compared to 16.0 months for all other patients — suggesting that co-occurring mutations may further worsen prognosis for certain patients. Notably, nearly all patients (96%) had prior CDK4/6 inhibitor exposure, and most went on to receive chemotherapy or elacestrant after ctDNA testing.
By the Numbers
Why it matters: While the study is hypothesis-generating and limited by its small, retrospective design, it highlights a potentially high-risk subgroup — those with ESR1 mutations and additional genomic co-alterations — who may benefit from tailored treatment sequencing and closer clinical attention going forward.
