AstraZeneca has reported results from a pre-specified subgroup analysis of the positive Phase III FALCON trial, indicating that treatment effects in terms of progression-free survival (PFS) were mostly consistent across the subgroups analysed with some possible exceptions, including patients with non-visceral disease.

This study analysed FASLODEX (fulvestrant) 500mg compared to ARIMIDEX (anastrozole) 1mg in the first line endocrine treatment of postmenopausal women who were initially diagnosed with locally advanced or metastatic breast cancer and who did not go through prior hormonal treatment for hormone receptor positive (HR+) breast cancer.

The study results indicated a decreased risk of progression by 41% in women whose disease has not spread to organs within the chest or abdomen when compared with ARIMIDEX.

Within this subgroup, the median PFS was 22.3 months for FASLODEX against 13.8 months for ARIMIDEX.

In patients suffering with visceral disease, the treatment impact for FASLODEX versus ARIMIDEX was comparable.

Serious adverse events (SAEs) in the non-visceral disease subgroup occurred in 11.6% of patients with FASLODEX in comparison to 16.8% of patients with ARIMIDEX.

In the visceral disease subgroup, SAEs occurred in 14.3% of patients with FASLODEX compared with 10.1% of patients with ARIMIDEX.

"The findings from this subgroup analysis build upon the existing body of clinical evidence for FASLODEX."

Aromatase inhibitors such as ARIMIDEX are the present standard of care in first-line treatment for postmenopausal women with HR+ advanced breast cancer.  

AstraZeneca executive vice president, global medicines development and chief medical officer Sean Bohen said: “The findings from this subgroup analysis build upon the existing body of clinical evidence for FASLODEX.

“AstraZeneca is committed to investigating the potential of FASLODEX in the first-line setting for women with advanced breast cancer, alongside the development of new targeted medicines and immunotherapies for women with all types of early and advanced breast cancer.”

University of Nottingham Royal Derby Hospital Centre professor of surgery John Robertson said: “This subgroup analysis has identified a cohort of patients with non-visceral disease who may derive even longer disease control from fulvestrant over anastrozole when compared to patients with visceral disease.

“Data from the FIRST trial, a head-to-head Phase II trial that showed both improved disease control and a survival benefit in favour of fulvestrant, corroborate the findings reported in the visceral and non-visceral subgroups in FALCON.

"Together, these findings indicate that fulvestrant may offer an important treatment option in advanced breast cancer for this population of patients.”

The trial met its primary endpoint and indicated a median PFS of 16.6 months in the FASLODEX arm against 13.8 months median PFS in the ARIMIDEX arm.

It found safety and tolerability profile in line with current experience with FASLODEX and ARIMIDEX.

The most commonly reported AEs in the FASLODEX and ARIMIDEX arms were arthralgia, hot flashes and nausea respectively.

AstraZeneca is seeking a label extension with US regulatory authorities to include the FALCON results in the FASLODEX label.

FASLODEX is currently approved as a monotherapy in the US for the treatment of HR+ metastatic breast cancer in postmenopausal women with disease progression following anti-estrogen therapy.

ARIMIDEX is presently approved in the US for the first-line treatment of postmenopausal women with HR+ or hormone receptor unknown locally advanced or metastatic breast cancer.

It is also approved for the treatment of advanced breast cancer in postmenopausal women with disease progression after tamoxifen therapy.