Last updated: August 15, 2026
Giredestrant (GDC-9545, RG6171) is an investigational next-generation oral selective estrogen receptor degrader (SERD) from Roche / Genentech, for estrogen-receptor-positive (ER-positive), HER2-negative breast cancer. It is a once-daily pill. As of August 2026 it is not yet FDA-approved — it is under FDA review (see below).
Mechanism of action:Giredestrant both blocks and degrades the estrogen receptor, shutting off the estrogen signaling that drives ER-positive breast cancer. Crucially, it stays active against ESR1-mutant tumors — the mutations that make cancers resistant to aromatase inhibitors — and, unlike fulvestrant (an injectable SERD), it is taken orally.
Regulatory status:Under FDA Priority Review for adjuvant early-stage (stage I–III) ER-positive, HER2-negative breast cancer (based on the Phase 3 lidERA trial) — FDA decision expected ~November 30, 2026. A second NDA, for giredestrant + everolimus in ESR1-mutated advanced disease (Phase 3 evERA), is also under review, decision expected ~December 2026. It is the first and only oral SERD with positive Phase 3 results in the curative (early-stage) setting.
Most breast cancer is ER-positive — it grows on estrogen. The standard way to treat it is endocrine (hormone) therapy: aromatase inhibitors (which lower estrogen) and fulvestrant (which degrades the estrogen receptor but must be given as a monthly injection into the muscle). Over time, many cancers develop ESR1 mutations that let them keep growing despite aromatase inhibitors — the point where endocrine therapy starts to fail.
What an oral SERD changes. Giredestrant is a pill that degrades the estrogen receptor and still works against ESR1-mutant tumors. That combines the mechanism of fulvestrant with the convenience of a daily tablet — and adds activity where standard endocrine therapy runs out of road.
The milestone. Several oral SERDs are in development, but they have all been tested in advanced/metastatic disease. Giredestrant is the first to succeed in the curative, early-stage setting: in the Phase 3 lidERA trial, adding adjuvant giredestrant reduced the risk of the cancer coming back (invasive disease recurrence) or death by about 30% versus standard adjuvant endocrine therapy. That result is the basis of the FDA Priority Review now underway, with a decision expected around November 30, 2026.
Giredestrant is not FDA-approved yet. Two New Drug Applications are under FDA review as of August 2026, each backed by a positive Phase 3 trial. Trial identifiers and settings below are verified against ClinicalTrials.gov; the regulatory dates are from Roche/Genentech announcements.
⏳ Priority Review — Adjuvant Early-Stage ER+/HER2- Breast Cancer (lidERA)
⏳ Under Review — Giredestrant + Everolimus, ESR1-Mutated Advanced Disease (evERA)
★ First Oral SERD Into the Curative Setting
Oral SERDs so far have all been advanced-disease drugs — elacestrant (Orserdu) is FDA-approved only for ESR1-mutated metastatic breast cancer. Giredestrant's lidERA result moves the class into early, potentially curable breast cancer for the first time, where the goal is preventing recurrence rather than controlling metastatic disease. If approved on the November 2026 decision, it would be the first oral SERD available in the adjuvant setting.
Giredestrant is investigational; it can only be received through a clinical trial or, if approved, by prescription after that date. Nothing here is a guarantee of approval.
The trials behind giredestrant's filings and program. lidERA and evERA (above) support the two NDAs; the trials below round out the Phase 3 program. NCTs, phases, settings, and enrollment are verified against ClinicalTrials.gov (August 2026).
Giredestrant trials actively recruiting as of August 2026 (corpus-verified). These are the ones a patient could potentially enroll in today.
Giredestrant is one of several next-generation endocrine agents racing to improve on aromatase inhibitors and injectable fulvestrant — especially in ESR1-mutant, endocrine-resistant disease. The class includes the FDA-approved oral SERD elacestrant (Orserdu) (ESR1-mutated advanced disease) and investigational agents imlunestrant, camizestrant, and the PROTAC estrogen-receptor degrader vepdegestrant (ARV-471). Giredestrant's distinguishing move is being first into the early-stage/adjuvant (curative) setting via lidERA. If your tumor is ER-positive, HER2-negative — particularly if it carries an ESR1 mutation after prior endocrine therapy — trials of these agents may be options.
Giredestrant is generally well tolerated as an oral endocrine therapy. Reported effects include fatigue, arthralgia (joint pain), and an asymptomatic slowing of the heart rate (sinus bradycardia) that has been observed in trials and is monitored during treatment. As with other endocrine agents, hot flashes and mild gastrointestinal effects can occur. The overall side-effect profile also depends on what giredestrant is combined with — for example a CDK4/6 inhibitor (which adds low blood counts and, for abemaciclib, diarrhea) or everolimus (which adds mouth sores and metabolic effects). This is general information, not a complete list — your oncologist can explain what to expect for a specific regimen.
What is giredestrant (GDC-9545) and how does it work?
Giredestrant (GDC-9545, RG6171) is an investigational next-generation oral selective estrogen receptor degrader (SERD) from Roche/Genentech. It is a once-daily pill that both blocks and degrades the estrogen receptor, shutting down the estrogen signaling that drives ER-positive breast cancer. Unlike aromatase inhibitors it stays active against ESR1-mutant tumors, and unlike fulvestrant (an injectable SERD) it is taken orally.
Is giredestrant FDA-approved?
Not yet. As of August 2026 giredestrant is investigational and under FDA review on two fronts: Priority Review for adjuvant early-stage ER-positive, HER2-negative breast cancer (Phase 3 lidERA), decision expected ~November 30, 2026; and a second application for giredestrant + everolimus in ESR1-mutated advanced disease (Phase 3 evERA), decision expected ~December 2026.
Why is giredestrant considered a first-in-class milestone?
It is the first and only oral SERD with positive Phase 3 results in the curative (early-stage/adjuvant) setting. In lidERA, adjuvant giredestrant reduced the risk of invasive disease recurrence or death by about 30% vs standard adjuvant endocrine therapy. Every other approved or filed oral SERD (such as elacestrant) has positive data only in advanced/metastatic disease.
Who might be eligible for a giredestrant trial?
Giredestrant trials are for ER-positive, HER2-negative breast cancer across early-stage and advanced settings; some target ESR1-mutant, endocrine-resistant disease. Recruiting trials as of August 2026 include pionERA (giredestrant vs fulvestrant, each with a CDK4/6 inhibitor, in previously-treated advanced disease) and a neoadjuvant trial of abemaciclib + giredestrant. Eligibility depends on ER/HER2 status, prior treatment, and stage — use the free ClinTrialFinder matcher to check.
What are the side effects of giredestrant?
Generally well tolerated: fatigue, arthralgia (joint pain), and an asymptomatic slowing of the heart rate (sinus bradycardia) monitored in trials; hot flashes and mild GI effects can occur. The profile also depends on the combination partner (a CDK4/6 inhibitor or everolimus).
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