Dr Rupert Bartsch shares his six key practice-relevant advances across early-stage, HER2-positive metastatic and triple negative breast cancer presented at ASCO 2026
Dr Rupert Bartsch (University of Vienna, Austria) share his perspectives on important studies across the breast cancer landscape presented at the 2026 American Society of Clinical Oncology (ASCO) Annual Meeting in Chicago. The studies below discuss interesting and strategic developments in genomic risk stratification in early disease, supportive care optimization, HER2-positive metastatic strategies and novel antibody–drug conjugates in triple-negative breast cancer.
touchONCOLOGY coverage of ASCO 2026
OPTIMA
→ Abstract 500: Stein RC, Andreas Makris A, Macpherson IR, et al. First results from the OPTIMA phase III randomized non-inferiority trial of test-directed chemotherapy in patients with high clinical risk ER-positive HER2-negative early breast cancer. Presented at: ASCO, Chicago, IL, USA. May 29 to June 2, 2026.
One of the most discussed early breast cancer studies at ASCO 2026 was the OPTIMA trial, a prospective randomized study evaluating whether treatment can safely be guided by the Prosigna/PAM50 Risk of Recurrence (ROR) score in patients with higher-risk hormone receptor-positive disease. Previous landmark studies such as MINDACT and RxPONDER established the role of genomic testing in lower-risk populations. OPTIMA pushes this further.
OPTIMA is particularly interesting because it included a much higher-risk population. Patients aged ≥40 years with up to nine positive lymph nodes were eligible and randomized either to standard chemo-endocrine therapy or treatment guided by genomic risk. Patients with a low ROR score were treated with endocrine therapy alone, while those with higher scores received chemotherapy followed by endocrine therapy.
Key clinical takeaways
Endocrine therapy alone was non-inferior in genomically low-risk patients, even among those with substantial nodal burden. This challenges the historical dogma that four or more positive nodes automatically mandate chemotherapy. Importantly, premenopausal patients in the trial largely received ovarian function suppression (OFS) alongside endocrine therapy, an important detail that reinforces the need for optimal endocrine intensification when chemotherapy is omitted.
REDUSE
→ Abstract 1004: Von Moos RA, Müller A, Hayoz S, et al. Prevalence of symptomatic skeletal events (SSE) with reduced denosumab (Dmab) dose density (every 12 weeks versus every 4 weeks): A randomized phase III non-inferiority trial SAKK 96/12 REDUSE. Presented at: ASCO, Chicago, IL, USA. May 29 to June 2, 2026.
Among the most immediately practice-relevant studies presented at ASCO 2026 was the Swiss REDUSE trial. The study assessed whether denosumab could be administered less frequently in patients with bone metastases from breast cancer or metastatic castration-resistant prostate cancer. Patients initially received standard denosumab (120 mg every 4 weeks) for three months before randomization to continue every 4 weeks and de-escalate to every 12 weeks.
The findings were clear:
- No difference in time to first skeletal-related event
- No efficacy compromise with de-escalation
- Numerically lower rates of:
- hypocalcemia
- osteonecrosis of the jaw
This is probably the most immediately practice-changing dataset from this year’s meeting. The implications are significant: lower treatment burden, fewer hospital visits and potentially improved safety.
PANKU-Breast02
→ Abstract LBA1003: Wu J, Zhang J, Ouyang Q, et al. Izalontamab brengitecan (iza-bren) versus physician’s choice of chemotherapy in patients with unresectable locally advanced or metastatic triple-negative breast cancer (TNBC): A randomized phase III study. Presented at: ASCO, Chicago, IL, USA. May 29 to June 2, 2026.
One of the most intriguing metastatic TNBC datasets presented at ASCO 2026 came from the PANKU-Breast02 trial, evaluating izalontamab brengitecan (iza-bren), a first-in-class bispecific antibody–drug conjugate targeting EGFR and HER3 with a topoisomerase I inhibitor payload, versus physician’s choice chemotherapy in pretreated metastatic triple-negative breast cancer.
The efficacy signal was striking:
- Median PFS improved from 3.1 months to 8.5 months
- Overall survival improved from 12.5 months to >15 months
- Response rates were also higher
The trade-off was toxicity. Grade ≥3 treatment-emergent adverse events and serious adverse events were more frequent with the ADC. This is not an easy drug, but it appears manageable, and the efficacy signal is certainly compelling. With first-line studies already underway, this could become an important addition to the TNBC treatment armamentarium.
OASIS-4
→ Abstract 512: Soares CN, Laapas K, Seitz C, et al. Effect of elinzanetant on sleep disturbance and aspects of quality of life in women with breast cancer experiencing vasomotor symptoms: OASIS-4 subgroup analysis by type of endocrine therapy. Presented at: ASCO, Chicago, IL, USA. May 29 to June 2, 2026.
Treatment adherence remains one of the major challenges in endocrine therapy, particularly because of vasomotor symptoms and sleep disruption. Dr Bartsch highlighted updated subgroup data from OASIS-4, evaluating elinzanetant, a neurokinin-1/3 receptor antagonist, for endocrine therapy-associated menopausal symptoms. The updated analysis focused specifically on sleep disturbance and postmenopausal quality of life. Both endpoints improved meaningfully with elinzanetant versus control. This may sound supportive rather than disease-focused, but improving tolerability is critical because adherence to endocrine therapy directly affects long-term outcomes. The data further support elinzanetant as a potentially important tool in managing endocrine-related toxicity.
HER2CLIMB-05
→ Abstract 1042: Dieras VC, Curigliano G, Martin M, et al. Tucatinib (TUC) combined with trastuzumab and pertuzumab (HP) as first-line (1L) maintenance therapy for HER2+ metastatic breast cancer (MBC): An in-depth safety analysis of HER2CLIMB-05. Presented at: ASCO, Chicago, IL, USA. May 29 to June 2, 2026.
In HER2-positive metastatic breast cancer, Bartsch highlighted new subgroup analyses from HER2CLIMB-05, evaluating the addition of Tucatinib to first-line trastuzumab plus pertuzumab. The primary analysis had already demonstrated a significant progression-free survival (PFS) benefit with tucatinib. At ASCO 2026, Veronique C Dieras presented outcomes by hormone receptor status, brain metastases, de novo versus recurrent metastatic disease. Benefit was seen consistently across all subgroups. Bartsch emphasized what may be the most clinically relevant observation: the role of endocrine therapy in HR+/HER2+ disease. Not all patients received concomitant endocrine treatment, and those who did achieved markedly prolonged PFS. In the tucatinib arm, PFS extended from approximately 12.6 months to over 27 months when endocrine therapy was added. This reinforces that HER2-positive disease is not biologically independent of estrogen receptor signaling. If the tumor is hormone receptor-positive, endocrine therapy matters. It is a reminder that endocrine maintenance should not be overlooked in this subgroup.
PALOMARES
→ Abstract 1017: Vernieri C, Caputo R, Dieci MV, et al. Effectiveness of first-line ET+CDK4/6i continuation beyond disease progression in a large cohort of patients with HR+/HER2− advanced breast cancer: Results from the multicenter, real-world, Italian study PALMARES-2. Presented at: ASCO, Chicago, IL, USA. May 29 to June 2, 2026.
Bartsch highlighted the Italian PALOMARES trial, a thought-provoking phase IV study exploring whether selected patients may benefit from continuing CDK4/6 inhibition beyond progression. Patients with oligoprogressive disease underwent local therapy and continued the same endocrine therapy plus CDK4/6 inhibitor rather than switching systemic treatment. Median post-progression PFS was 10.5 months, with an apparent overall survival advantage versus patients who discontinued therapy.
Importantly, this was not a randomized comparison, so selection bias is a major limitation. Still, the concept is clinically interesting. This is certainly not a new standard, but it supports the idea that in carefully selected patients, ablating isolated progression and maintaining otherwise effective systemic therapy may be reasonable.
This content has been developed independently by Touch Medical Media for touchONCOLOGY in collaboration with Dr Rimas Lukas. Views expressed are the speaker’s own and do not necessarily reflect the views of Touch Medical Media.
Disclosure: Dr Rupert Bartsch is a consultant for: Amgen, Astra-Zeneca, BMS, Daiichi-Sankyo, Eisai, Eli-Lilly, Gilead, Gruenenthal, MSD, MedMedia, Novartis, Pfizer, Pierre-Fabre, Roche, Stemline. He has received grant/research support from, is a member of the Advisory Board for, and has received honoraria/honorarium from: Daiichi-Sankyo, Astra Zenca, MSD. He has received travel support: Astra-Zeneca, Daiichi-Sankyo, Eli-Lilly, Gilead, MSD, Novartis, Pfizer, Roche.
Cite: Breast Cancer at ASCO 2026: Six key insights. touchONCOLOGY. 14th June 2026.
Editor: Sophie Nickelson, Editorial Director
