Breast Oncology Briefing

Weekly. Updated automatically every Monday morning.

Week of September 28 to October 5, 2026

Giredestrant plus everolimus evERA data published in NEJM

Note on the calendar: this is a between-congress week, and a relatively light one. The ESMO Congress runs in Madrid from October 23 to 27, 2026 (venue program), roughly three weeks out, with SABCS behind it in December. Nothing from a major meeting landed inside this window, so this edition is built around journal publications and regulatory actions.

Practice-Relevant Clinical

Lead item: evERA phase 3 results published in NEJM

This is the clear lead for the week. On September 30 and October 1, Genentech and Roche announced that detailed results from evERA Breast Cancer (NCT05306340) were published in the New England Journal of Medicine, and both releases carry the full statistics.

Design: a phase 3, randomized, open-label, multicenter trial of giredestrant (investigational oral SERD) plus everolimus versus standard endocrine therapy plus everolimus in ER-positive, HER2-negative locally advanced or metastatic breast cancer with progression or recurrence after a CDK4/6 inhibitor plus endocrine therapy, in either the adjuvant or advanced setting.

Findings: In the ESR1-mutated population, median PFS was 10.0 months with giredestrant plus everolimus versus 5.5 months in the comparator arm (stratified HR = 0.38, 95% CI: 0.27-0.54, p<0.001). In the intent-to-treat population, median PFS was 8.8 versus 5.5 months (HR = 0.56, 95% CI: 0.44-0.71, p<0.001), corresponding to risk reductions of 62% and 44% in the two populations. Overall survival was immature, with positive but statistically unconfirmed trends: ITT HR = 0.69 (95% CI: 0.47-1.00) and ESR1-mutated HR = 0.62 (95% CI: 0.38-1.02); follow-up continues to the next analysis. Safety was described as manageable and consistent with the known profiles of the components, with no unexpected findings, no photopsia, and low rates of bradycardia. Additional ASCO 2026 analyses (pre-window) showed benefits in PFS2 and chemotherapy-free survival.

Skeptical read: the trial was open-label, and the OS curves are the standard caution here: an impressive PFS in a post-CDK4/6i population with OS confidence intervals that include 1.0.

Practice implication: giredestrant is not prescribable yet. The FDA has accepted the NDA for giredestrant plus everolimus in ER-positive, HER2-negative, ESR1-mutated locally advanced or metastatic breast cancer after endocrine therapy, with a decision expected by December 18, 2026. If approved, it would be the third new ESR1-gated endocrine option to reach the market this year, following camizestrant plus a CDK4/6 inhibitor (approved September 4) and imlunestrant plus abemaciclib (approved September 18, both pre-window), but the only one paired with mTOR inhibition in the post-CDK4/6i space. Sequencing across these three will be a live question for tumor boards through year end.

Sources: Genentech press release, September 30, 2026; Roche media release, October 1, 2026.

npj Breast Cancer review: operationalizing ESR1 and pathway resistance testing

A practical review by Mouabbi and Cecchini, published open access on October 2 in npj Breast Cancer, addresses a problem the recent approvals have made urgent: the new SERD-class labels are gated on ESR1 mutation detection, and the patients who most need testing are the hardest to test. The authors note ESR1 mutations are present in approximately 30-40% of patients with endocrine-resistant HR-positive/HER2-negative advanced disease and PI3K/AKT/PTEN pathway alterations in up to 50%. They walk through three multidisciplinary scenarios: bone-only progression without ctDNA reimbursement, testing on archival primary tissue that misses the timing of resistance acquisition, and a false-negative ctDNA result from low tumor fraction rescued by reflex pleural effusion cytology.

Practice implication: with three ESR1-gated FDA actions in 2026 and the Guardant360 CDx assay approved as the companion diagnostic for the camizestrant, imlunestrant, and vepdegestrant labels, ESR1 testing logistics are now a clinic-level process problem, not a theoretical one. This piece is a useful scaffold for building reflex-testing pathways, particularly for APPs who see the bone-only progression patient before the treating oncologist does.

Source: Mouabbi JA, Cecchini M, npj Breast Cancer, published October 2, 2026.

FDA Landscape

The honest headline first: no new breast oncology approvals, complete response letters, or advisory committee actions landed inside this window. My searches of FDA announcements and company newsrooms turned up none dated September 28 through October 5. The two SERD-class approvals dominating recent discussion, camizestrant (Etcamah, September 4) and imlunestrant plus abemaciclib (Inluriyo, September 18), predate this window and are covered above only as context for evERA and sequencing.

Elinzanetant sNDA accepted with priority review

On September 28, Bayer announced the FDA accepted a supplemental NDA and granted priority review for elinzanetant (Lynkuet) for moderate to severe vasomotor symptoms in women receiving endocrine therapy for the treatment or prevention of HR-positive breast cancer. This would be the first FDA-approved option for endocrine-therapy-associated VMS in this population; none currently exists in the US. Clinical detail is covered in the Survivorship section below. Note: Bayer's release does not state a PDUFA date; priority review sets a six-month review goal, but I am not asserting a specific action date because none was published.

Sources: Bayer press release via BioSpace, September 28, 2026; OncLive coverage.

Giredestrant PDUFA dates to track

Roche's October 1 release confirms two pending dates: November 30, 2026 for the adjuvant NDA (giredestrant monotherapy for stage I-III ER-positive, HER2-negative breast cancer, based on lidERA, under priority review) and December 18, 2026 for the advanced-disease NDA (giredestrant plus everolimus, ESR1-mutated, based on evERA). I found no evidence this week that either previously communicated date has slipped; flag me if you have heard otherwise and I will verify against the primary sources.

Survivorship / Supportive Care

Elinzanetant: OASIS-4 and the endocrine-therapy VMS gap

The clinical foundation of the sNDA accepted September 28 is OASIS-4 (NCT05587296): a 52-week, double-blind, randomized, placebo-controlled phase 3 trial at 90 sites outside the US. A total of 474 women aged 18-70 with moderate to severe VMS associated with endocrine therapy for HR-positive breast cancer or its prevention were randomized 2:1 to elinzanetant for 52 weeks (n=316) or placebo for 12 weeks followed by elinzanetant for 40 weeks (n=158). Elinzanetant met the primary endpoints, significant reductions in mean daily frequency of moderate to severe VMS from baseline to weeks 4 and 12 versus placebo, and met all secondary endpoints including VMS severity at weeks 4 and 12, week 1 frequency reduction, and improvements in sleep disturbance and menopause-related quality of life, with effects maintained over the study period. Results were presented at ASCO 2025 and published in NEJM in June 2025. Common adverse events were headache, fatigue, and somnolence; during the 12-week placebo-controlled period, somnolence, fatigue, and diarrhea were more frequent with elinzanetant. Elinzanetant is a dual neurokinin NK-1/NK-3 receptor antagonist, non-hormonal, already approved for menopause-associated VMS (October 2025) and already indicated for adjuvant endocrine therapy-related VMS in Canada, the UK, and Switzerland.

Practice implication: VMS on adjuvant endocrine therapy is one of the most common adherence-limiting problems APPs manage, and current pharmacologic options are either non-FDA-approved for this population or hormonal. If approved, this would fill a genuine labeled gap, including for women on risk-reducing endocrine therapy. Watch for the priority review decision; no PDUFA date has been published.

Source: Bayer press release; Contemporary OB/GY, September 28, 2026.

SUPREMO: 5-year quality-of-life results

The Lancet Oncology has published 5-year QOL results from the SUPREMO randomized phase 3 QOL substudy (UK patients within the international trial of post-mastectomy chest wall radiotherapy in intermediate-risk breast cancer, ISRCTN61145589). Of 1,233 UK patients, 989 consented to the substudy. At 5 years, chest wall symptoms were significantly worse with radiotherapy (effect estimate 1.99, 95% CI: 0.36-3.62; p=0.017), with improvement between years 1, 2, and 5. Chemotherapy was associated with less improvement over time (effect estimate 2.97, 95% CI: 0.24-5.71; p=0.033), without interaction with radiotherapy. No significant differences were seen in arm symptoms, body image, fatigue, pain, overall QOL, physical functioning, anxiety, or depression. A subgroup with sentinel node biopsy followed by axillary clearance plus radiotherapy had worse chest wall symptoms (difference -5.29, 95% CI: -8.53 to -2.05; p=0.0015). Context: SUPREMO previously showed no 10-year overall survival benefit from chest wall radiotherapy in this intermediate-risk population. Caveat: I could not confirm the exact online publication date from the retrieved page text, so treat the timing as this week pending verification; the statistics above are taken directly from the Lancet Oncology article.

Practice implication: supports counseling patients with intermediate-risk post-mastectomy disease that omitting chest wall radiotherapy trades no demonstrated survival benefit for measurably less long-term chest wall toxicity, and flags the sentinel-then-clearance subgroup as highest risk for persistent symptoms.

Source: The Lancet Oncology.

Translational / Horizon

Guardrail: nothing in this section is practice-changing today. These are early signals and commentary, not treatment options.

Vepdegestrant as proof of concept for protein degradation

A commentary in Medicinal Chemistry Research, surfaced October 3, examines vepdegestrant (Veppanu, FDA-approved May 2026, pre-window) as the first FDA-approved heterobifunctional oral PROTAC in oncology. The argument is less about this drug, which now sits in an increasingly crowded ESR1-mutated space, than about platform validation: demonstrating that a large, structurally complex E3-ligase-directed degrader can be made orally bioavailable and can clear a full regulatory bar. For a breast oncology audience, the near-term relevance is the pipeline behind it, degrader programs against ER and other resistance targets that now have a clinical precedent to cite.

Source: OncoDaily summary, October 3, 2026.

Boron neutron capture therapy in recurrent TNBC, first-in-Taiwan series

National Tsing Hua University reported on September 28 that, with two hospital partners, it has completed compassionate-use BNCT in five patients with recurrent triple-negative breast cancer, observing significant tumor reduction with limited damage to surrounding normal tissue. The 70.2% objective response rate quoted in the release refers to the program's overall compassionate-use experience across 437 cases, mostly brain and head-and-neck tumors, not to the breast cohort. This is a single-institution press release with five breast patients and no peer-reviewed breast-specific outcomes; BNCT is being used as local salvage. Interesting as a signal of where high-LET targeted radiotherapy is heading for locally refractory disease, and nothing more.

Source: NTHU announcement, September 28, 2026.

Cuts Made (held back or omitted, ask for more if any of these matter to you):

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