Breast Cancer Patients With Estrogen Receptor Mutations Benefit From Switch to Fulvestrant

Patients with breast cancer treated with an aromatase inhibitor plus palbociclib (Ibrance) could benefit from an early switch to fulvestrant (Faslodex) plus palbociclib if they display a rising estrogen receptor gene (ESR1) mutation in their blood before disease progression. This patient group was found to double their median progression-free survival (PFS) after the switch, according to results from the phase 3 PADA-1 clinical trial presented at the San Antonio Breast Cancer Symposium.

“Fulvestrant remains effective against receptors with these mutations, but it provides limited progression-free survival benefit when used as a second-line therapy,” François-Clément Bidard, MD, PhD, a professor of medical oncology at Institut Curie and Paris-Saclay University, said in a press release. “Our goal was to track the emergence of ESR1 mutations in patients’ blood during first-line therapy and act on them as soon as they appeared, before they led to an actual clinical progression of the disease.”

After a median follow up of 26 months, the median PFS rate for those who switched to fulvestrant was more than twice as long (11.9 months) as those who remained on aromatase inhibitors (5.7 months).

Patients who progressed after continuing aromatase inhibitor treatments could switch over to fulvestrant, and investigators found that the median PFS of individuals who switched was 3.5 months.

This supports other studies that showed a short benefit of fulvestrant when used as a second-line treatment, according to the study. The PADA-1 trial included 1017 patients with ERα-positive breast cancer who did not have overexpression of the growth factor receptor HER2 and were treated with a first-line aromatase inhibitor plus palbociclib.

Of these patients, 407 experienced disease progression in the absence of an ESR1 mutation, which was only detected in 279 patients prior to or concurrent with disease progression.

Only those who did not experience concurrent disease progression (219 individuals) were randomly assigned either to continue aromatase inhibitor plus palbociclib (84) or switch to fulvestrant plus palbociclib (88).

A limitation of the study was investigators were not blinded to which treatment arm the individuals were randomized to.

Reference

Breast cancer patients with estrogen receptor mutations may benefit from early switch to fulvestrant/palbociclib. San Antonio Breast Cancer Symposium. News release. November 30, 2021. Accessed on December 1, 2021. Email.