Week of October 19 to October 26, 2026
Iza-Bren Headlines Three Phase 3 ADC Wins at ESMO
Note on the week: The ESMO Congress 2026 is underway in Madrid, October 23 to 27. This edition covers the first three days of breast data, which delivered three positive phase 3 ADC readouts, and closes with the October 26 rapid oral session on ADC sequencing and resistance.
Practice-Relevant Clinical
PANKU-Breast01: izalontamab brengitecan in post-chemotherapy HR+/HER2- disease (the lead)
The lead development this week is the first phase 3 readout of izalontamab brengitecan (iza-bren, BL-B01D1), a bispecific EGFR x HER3 ADC with a topoisomerase I payload, developed by SystImmune with Bristol Myers Squibb. PANKU-Breast01 (NCT06343948) randomized 383 patients 1:1 at 72 centers in China with unresectable locally advanced, recurrent, or metastatic HR+/HER2- breast cancer to iza-bren or physician's choice chemotherapy. Eligibility required prior endocrine therapy, a CDK4/6 inhibitor, a taxane, and one or two prior chemotherapy lines, with ECOG 0-1. No EGFR or HER3 testing was required.
At a median PFS follow-up of 15.2 months, median PFS by blinded independent central review was 8.2 months (95% CI, 6.9-8.6) with iza-bren versus 4.0 months (95% CI, 2.9-4.3) with chemotherapy (HR 0.41; 95% CI, 0.33-0.53; p<0.0001). Confirmed ORR was 40.5% (95% CI, 33.5-47.9) versus 20.2% (95% CI, 14.8-26.6), disease control rate 86.3% versus 63.7%, and median duration of response 6.9 versus 4.2 months. Benefit was consistent across subgroups, including two prior chemotherapy lines (HR 0.31; 95% CI, 0.20-0.50) and baseline liver metastases (HR 0.40; 95% CI, 0.30-0.53). OS was immature at a median follow-up of 17.8 months, with no detrimental effect observed.
The safety data warrant close attention for anyone contemplating eventual clinical use: grade 3 or higher treatment-related AEs occurred in 85.3% versus 65.8% with chemotherapy, and treatment-related serious AEs in 41.6% versus 11.4%. Grade 3 or higher neutropenia (53.7%), anemia (49.5%), leukopenia (48.4%), and thrombocytopenia (46.3%) dominated; 73% of iza-bren patients received platelet-elevating agents and 15% required platelet transfusion. Dose reductions were needed in 64.7%, though discontinuation for toxicity was only 1.6%, and adjudicated ILD occurred in two patients (1.1%, grade 1-2). The results were presented October 23 (LBA50) and published simultaneously in The Lancet.
Practice implication: Nothing changes in US prescribing today, but this is the strongest signal yet that a new target class (EGFR x HER3, biomarker-unselected) is entering the post-chemotherapy HR+/HER2- space where sacituzumab govitecan is the only approved ADC, and it is worth flagging for trial-referral conversations. Sources: BMS/SystImmune release and OncoLive report with full toxicity detail.
HORIZON-Breast06: trastuzumab rezetecan in HER2-low, chemotherapy-naive advanced disease
Published in JAMA on October 23 and presented as LBA13, this open-label phase 3 trial randomized 551 women with HER2-low unresectable or metastatic breast cancer at 73 centers in China to the HER2-directed topo I ADC trastuzumab rezetecan or physician's choice chemotherapy. Patients had received no more than one prior chemotherapy line in the metastatic setting, and HR-positive patients had prior endocrine therapy. Both primary endpoints were met: in chemotherapy-naive patients, median PFS was 16.6 versus 6.8 months (HR 0.25; 95% CI, 0.19-0.33), and in the overall population 16.4 versus 6.8 months (HR 0.27; 95% CI, 0.21-0.34), both p<0.001. Hematologic toxicity was more common with the ADC and dose modifications were frequent, while ILD incidence was low. Practice implication: T-DXd is currently approved in HER2-low disease after prior chemotherapy; a 16-month PFS in a chemotherapy-naive population sets up a direct challenge to the current sequence, where ADCs come after endocrine therapy and one or more chemotherapy lines. Sources: JAMA media release and Medscape report.
APEX-Breast01: TQB2102, a biparatopic HER2 ADC, in HER2-low recurrent/metastatic disease
Presented October 23 as LBA27, this phase 3 trial from Chia Tai Tianqing (Sino Biopharmaceutical) randomized 543 patients with HER2-low (IHC 1+ or 2+/ISH-) recurrent or metastatic breast cancer, chemotherapy-naive in the advanced setting, 1:1 to TQB2102 7.5 mg/kg every 3 weeks or physician's choice chemotherapy (capecitabine, paclitaxel, or nab-paclitaxel). HR-positive patients (461 of 543, 91.3% previously CDK4/6 inhibitor-treated) had progressed on at least one endocrine line; HR-negative patients had CPS below 1 or unknown. In the HR+/HER2-low primary population (n=228 vs 233), median PFS by blinded independent review was 16.4 versus 5.5 months (HR 0.29; 95% CI, 0.22-0.39; p<0.0001). In the overall population, median PFS was 16.4 versus 5.5 months (HR 0.29; 95% CI, 0.22-0.38), ORR 68.8% versus 31.0%, median duration of response 15.0 versus 7.1 months, and clinical benefit rate 78.8% versus 44.2%. OS trends favored TQB2102 (HR 0.44 overall; 0.47 in HR+) but remain immature. In the small HR-/HER2-low cohort (n=41 per arm), median PFS was 8.5 versus 5.4 months (HR 0.27) and ORR 80.5% versus 29.3%. Grade 3 or higher neutropenia was 30.1% versus 23.3%; treatment-related ILD was 2.2% with no ILD deaths. Practice implication: Nearly identical PFS to HORIZON-Breast06 in an overlapping population with a different molecule reinforces that next-generation HER2 ADCs are converging on the HER2-low, pre-chemotherapy space. Sources: Sino Biopharmaceutical announcement and conference summary.
I-SPY2.2 RT-DXd arm: rilvegostomig plus T-DXd neoadjuvant strategy published
JAMA Oncology published the I-SPY2.2 RT-DXd arm on October 22: 182 adults with high-risk stage II/III ERBB2-negative early breast cancer (ERBB2-low/ultralow, IHC 0-2+) across 30 US sites were adaptively randomized; block A was up to 4 cycles of rilvegostomig 750 mg plus T-DXd 5.4 mg/kg, followed by taxane-based block B and AC-based block C as needed. In 105 evaluable block A patients, the modeled pCR rate was 54% in immune-positive tumors (meeting the prespecified success threshold), 57% in HR-positive/immune-positive and 52% in HR-negative/immune-positive disease. Among immune-positive patients achieving pCR, 21 (62%) required only block A and 33 (97%) avoided anthracycline. Immune-negative tumors responded poorly. ILD occurred in 13 of 105 (12.4%), one grade 3, with enrollment paused twice and early detection via serial CT. Practice implication: phase 2 and biomarker-defined, so not practice-changing, but it is the clearest proof of concept yet for anthracycline-free neoadjuvant ADC plus bispecific strategies in ERBB2-negative disease. Source: JAMA Oncology.
Honest framing for the week: all three phase 3 ADC trials were conducted in China, are open-label against physician's choice chemotherapy with no active ADC comparator, and have immature OS. They reshape the pipeline rather than this week's prescriptions.
FDA Landscape
A quiet week: no breast oncology approvals, complete response letters, or advisory-committee actions fell between October 19 and 26. The FDA's oncology approval notifications page confirms the most recent breast action was October 7 (below). No breast-relevant advisory committee appears on the FDA advisory committee calendar.
Context from just before the window: on October 7 the FDA approved tucatinib with trastuzumab and pertuzumab as chemotherapy-free maintenance after 4 to 8 cycles of THP induction, based on HER2CLIMB-05 (n=654): median PFS 24.9 months (95% CI, 21.3 to not reached) versus 16.3 months (95% CI, 12.6-18.7); HR 0.64 (95% CI, 0.51-0.80); p<0.0001. Pfizer's label notes increased severity of hepatotoxicity versus the known profile, with serious hepatotoxicity in 3.9% and one fatal drug-induced liver injury. Details: FDA notice.
Watch list, with dates confirmed against primary sources: giredestrant has two PDUFA dates ahead. The adjuvant NDA (lidERA, priority review) has a goal date of November 30, 2026, and the ESR1-mutant advanced-disease NDA with everolimus is due December 18, 2026, per Roche's October 1 release and the pdufa.bio cancer tracker. As reported by Small Molecule News, lidERA randomized 4,170 patients with invasive disease-free survival HR 0.70 and a 3-year rate of 92.4% versus 89.6%. If approved, giredestrant would be the first oral SERD in early breast cancer and the first oral ER degrader approved without an ESR1-mutation requirement; the four currently approved oral ER drugs (elacestrant, imlunestrant, vepdegestrant, camizestrant) all carry ESR1-restricted indications.
Expectation-setting correction: the first-line oral SERD space has already broken with expectations this year. Giredestrant's persevERA (announced March 9, 2026) and camizestrant's SERENA-4 (1,371 patients, September 11, 2026) both missed their PFS endpoints against an aromatase inhibitor plus palbociclib, even as SERENA-6 (maintenance switch upon emergent ESR1 mutation, 16.0 versus 9.2 months) earned camizestrant accelerated approval on September 4. Separately, Olema's palazestrant OPERA-01 topline was moved to the first quarter of 2027 from the second half of 2026 in the company's August 10 report, so no readout this quarter.
Survivorship / Supportive Care
Oxaloacetate for cancer-related cognitive impairment
A UCLA phase 2 study published in JCO Oncology Advances (DOI 10.1200/OA-26-00063) enrolled 18 women with early-stage breast cancer one to five years past diagnosis reporting significant cognitive impairment (mean age about 50, most with prior chemotherapy, roughly 90% on endocrine therapy). Oxaloacetate 500 mg twice daily for 8 weeks; 16 of 18 completed. All 16 reported improvement in cognitive symptoms, with the primary perceived cognitive impairment measure rising from 29.1 at baseline to 55.5 at 8 weeks, moving the group from the impaired to the normal range, plus reduced fatigue (including mental fatigue) and improved physical functioning; neuropsychological testing showed gains in processing speed and executive function, which the authors call preliminary. GI symptoms were the main toxicity and two participants discontinued. Caveat, stated plainly: single-arm, 18 patients, no placebo; a randomized placebo-controlled phase 2 is expected to open in late 2026. Treat this as a signal to watch, not something to recommend. Source: report with study detail.
Also of nursing interest: a photovoice study in Seminars in Oncology Nursing (published October 22) documents how chemotherapy-induced peripheral neuropathy shapes daily quality of life in breast cancer survivors, a useful qualitative complement when counseling patients whose CIPN is dismissed as minor. Otherwise this section is light this week.
Translational / Horizon
Guardrail: nothing in this section is practice-changing today. These are early signals about where ADC development and resistance biology are heading.
ADC sequencing and resistance, from the October 26 ESMO rapid oral session
- SWITCH (NCT06649331): Fudan University Shanghai Cancer Center assigned 54 patients with HER2-negative metastatic breast cancer, 94.4% previously exposed to a topoisomerase I ADC, to one of four Hengrui conjugates against different antigens but the same payload class. Confirmed response rates were 0%, 8.3%, 0%, and 5%, and responses occurred only in patients moving from disitamab vedotin (an MMAE conjugate) to a topoisomerase I agent. This is among the cleanest clinical evidence yet that cross-resistance tracks with payload more than antigen.
- Payload switching: Mabwell's nectin-4 MMAE conjugate bulumtatug fuvedotin produced a 30.0% response rate in 60 evaluable triple-negative patients, all previously treated with a topoisomerase I conjugate, supporting the payload-rotation concept.
- Mechanism data: Paolo Tarantino presented paired pre-treatment and progression biopsies from 26 patients. HER2 protein fell in 8 of 14 patients after T-DXd but none became HER2-null, and tumors exposed to sacituzumab govitecan showed no consistent TROP2 loss. More than half showed proteomic increases in the efflux transporters ABCB1 and ABCC1 or shifts in DNA damage response and trafficking proteins, arguing that target retention plus drug efflux, not antigen loss, drives much acquired ADC resistance.
A related structural observation from APO/APE News's analysis of the ESMO late-breakers: none of the breast ADC phase 3 programs selected patients on their nominal targets (no EGFR or HER3 test for iza-bren), signaling a drift toward biomarker-agnostic ADC development that will eventually force the field to decide who does not need these drugs.
Cuts Made: the full evERA giredestrant readout (NEJM, September 30, outside the window; referenced here only as FDA context); TROPION-Breast02 PRO and CNS subgroup data from ESMO Breast 2026 (May, outside the window); a qualitative Faroese survivorship study (Frontiers in Oncology, October 22, held for length); the ASCO Post October 25 recap of recent approvals (secondary coverage); and non-breast ESMO 2026 late-breakers (VOLGA, OptiTROP-Lung06, G-HOPE-001, TAISHAN-301, others). Ask if you want any of these expanded.