GIRE Combination Shows PFS Benefit in First-Line Metastatic Breast Cancer Treatment, Earning FDA Priority Review

The large phase 3 persevERA Breast Cancer trial (NCT04546009) evaluated giredestrant (GIRE; Roche)—a next-generation oral selective estrogen receptor (ER) antagonist and degrader—plus palbociclib (PALBO, Ibrance; Pfizer) as first-line therapy for ER-positive (ER+), HER2-negative (HER2–) locally advanced or metastatic breast cancer (LA/mBC). The combination produced a numerically meaningful improvement in progression-free survival (PFS) over the current standard of letrozole plus PALBO. However, the trial did not meet the predefined statistical significance threshold.

As a result of these data, the FDA granted the GIRE combination priority review for the adjuvant treatment of adults with ER+/HER2– stage I, II, and III breast cancer. The FDA is expected to make a decision on the approval by November 30, 2026.¹

“The combination of endocrine therapy with a CDK4/6 inhibitor is the standard of care for first-line treatment of patients with ER+, HER2– advanced breast cancer. Giredestrant is a potent, next-generation, fully oral ER antagonist designed to drive deep and sustained inhibition of ER signaling,” said Nicholas C. Turner, MD, PhD, consultant medical oncologist at the Royal Marsden Hospital and Institute of Cancer Research in London, England.²

“In 2 phase 3 clinical trials, giredestrant has demonstrated superior efficacy compared [with] standard-of-care endocrine therapy—as adjuvant therapy in the lidERA trial [NCT04961996] and in combination with everolimus post CDK4/6 inhibition for advanced breast cancer.”²

ER+/HER2– Metastatic Breast Cancer and GIRE

Breast cancer remains the most frequently diagnosed malignancy among women, representing nearly 1 in 3 new cancer cases in female patients. Over recent decades, treatment has been fundamentally reshaped by the identification of molecular biomarkers and distinct tumor subtypes—a shift that has moved oncology away from a one-size-fits-all approach and toward therapies precisely matched to disease biology.³

While ER-positive breast cancer is the most common subtype, its metastatic form is far from straightforward to manage. Resistance to endocrine therapy (ET) remains one of the field’s most persistent obstacles, eroding the effectiveness of standard treatments over time and reinforcing the urgency of developing therapies that can overcome or circumvent these resistance mechanisms.⁴

GIRE, an oral selective ER degrader (SERD) and antagonist, may help address the gap left by resistance to ET. Rather than simply blocking estrogen, GIRE takes a more aggressive approach by binding to the estrogen receptor and triggering its destruction, cutting off a key driver of tumor growth at the source.

What sets it apart from older hormone-blocking agents is not just how it works but how it is taken. Patients take the treatment as a daily oral tablet rather than a monthly injection, lowering the treatment burden while potentially offering activity in tumors that have already become resistant to earlier therapies.⁴

Evaluating GIRE in the persevERA Trial

The persevERA BC trial enrolled 992 patients with de novo or recurrent LA/mBC who had received no prior systemic therapy for metastatic disease. Participants were randomly assigned 1:1 to receive either GIRE (30 mg daily) plus palbociclib or letrozole (2.5 mg daily) plus palbociclib, each on 28-day cycles. Pre- and perimenopausal women and men also received a luteinizing hormone–releasing hormone agonist.⁵

The patient population was broadly representative of clinical practice. The median age was 63 years; approximately 80% of patients were postmenopausal, 60% had visceral disease, and nearly 70% had relapsed more than 12 months after completing adjuvant therapy.⁵

Median PFS Promising With GIRE

With a median follow-up of 52.2 months and 623 investigator-assessed PFS (INV-PFS) events recorded at the January 2026 data cutoff, the trial did not meet its primary end point. The HR for INV-PFS was 0.89 (95% CI, 0.76-1.05; P = .1553). Nevertheless, the absolute difference was clinically notable: The median INV-PFS was 33.1 months with GIRE plus PALBO compared with 28.2 months with letrozole plus PALBO—a difference of approximately 5 months.⁵

GIRE Safety Profile Is Favorable

The safety profile of GIRE in combination with palbociclib was consistent with the known profiles of each individual agent. The most common grade 3 to 4 adverse events (AEs) in the GIRE arm were hematologic abnormalities, a well-characterized effect attributable to palbociclib. Discontinuation rates due to AEs were low and comparable between arms—6.5% in the GIRE group vs 5.5% in the letrozole group—suggesting the combination is well tolerated in the long-term.⁵

The Future of GIRE

GIRE has shown promising activity in other settings. In the adjuvant setting, the lidERA Breast Cancer trial data demonstrated superior efficacy over standard endocrine therapy, and in the post–CDK4/6 inhibitor metastatic setting, the evERA Breast Cancer trial (NCT05306340) data showed benefit when combined with everolimus. The persevERA Breast Cancer results add nuance: Although GIRE did not statistically outperform letrozole as a CDK4/6 inhibitor partner in unselected first-line patients, the roughly 5-month numerical gain in median PFS is not trivial and leaves open questions about potential benefit in specific subgroups.

Investigators are now evaluating GIRE in the ongoing pionERA Breast Cancer study (NCT06065748), which is testing GIRE vs fulvestrant—both combined with physician’s choice of CDK4/6 inhibitor—in patients who have relapsed on adjuvant endocrine therapy or present with a short treatment-free interval of less than 12 months. That study may help define where GIRE best fits within the evolving breast cancer treatment landscape.

REFERENCES

1. FDA accepts new drug application for Genentech’s giredestrant in ER-positive early-stage breast cancer, the first and only oral SERD with positive phase III results in the curative setting. News release. Genentech. June 2, 2026. Accessed June 2, 2026. https://www.biospace.com/press-releases/fda-accepts-new-drug-application-for-genentechs-giredestrant-in-er-positive-early-stage-breast-cancer-the-first-and-only-oral-serd-with-positive-phase-iii-results-in-the-curative-setting

2. Kalinsky K, Lim B, Sanders Clark A, et al. Breast Cancer—Metastatic. Presented at: 2026 American Society of Clinical Oncology Annual Meeting; May 29-June 2, 2026; Chicago, IL.

3. Key statistics for breast cancer. American Cancer Society. Updated May 5, 2025. Accessed December 4, 2025. https://www.cancer.org/cancer/types/breast-cancer/about/how-common-is-breast-cancer.html

4. Metastatic ER-positive, HER2-negative breast cancer: novel treatment combination improves progression-free survival. ASCO Post. Updated November 3, 2025. Accessed June 2, 2026. https://ascopost.com/news/october-2025/metastatic-er-positive-her2-negative-breast-cancer-novel-treatment-combination-improves-progression-free-survival/ 

5. Turner NC, Jhaveri KL, Bardia A, et al. Giredestrant (GIRE) + palbociclib (PALBO) vs letrozole (LET) + PALBO as first-line (1L) therapy in patients (pts) with estrogen receptor–positive, HER2-negative locally advanced or metastatic breast cancer (ER+, HER2– LA/mBC): primary analysis of the phase III persevERA BC trial. Presented at: 2026 American Society of Clinical Oncology Annual Meeting; May 29-June 2, 2026; Chicago, IL. Abstract LBA1006.