ESMO Congress 2026 Breast Cancer: 10 Abstracts to Watch

The breast cancer programme at ESMO Congress 2026 brings together several studies with the potential to clarify some of the most active questions in contemporary breast oncology. The official programme spans early and advanced disease, with late-breaking phase III trials, mature overall survival analyses, post-CDK4/6 strategies, biomarker studies, and a rapidly expanding focus on antibody–drug conjugate sequencing.

The selection below is based on the official ESMO 2026 final programme updated September 28, 2026. Where the programme provides the study title but not the numerical results, no efficacy outcome is inferred before official presentation.

TALENT: Taking T-DXd Into HER2-Low, HR-Positive Early Breast Cancer

LBA23 — TALENT will report the final results of a neoadjuvant study evaluating trastuzumab deruxtecan (T-DXd) with or without anastrozole, or in sequence with chemotherapy, in HER2-low, HR-positive early-stage breast cancer. Sara Hurvitz is listed as the presenting first author (Hurvitz et al., 2026).

TALENT is particularly relevant because it moves an ADC strategy into the curative-intent setting of HER2-low disease. The study design also addresses more than one therapeutic question: whether T-DXd can generate meaningful neoadjuvant activity in this biological population, whether endocrine therapy contributes when combined with the ADC, and how an ADC might be positioned relative to conventional chemotherapy.

The final results should therefore be interpreted not only through tumor response but through what they may suggest about the future architecture of systemic therapy for HER2-low early breast cancer.

NATALEE: Six-Year Follow-Up Moves the Discussion Toward Overall Survival

LBA25 — NATALEE will present six-year overall survival and efficacy outcomes with adjuvant ribociclib plus a nonsteroidal aromatase inhibitor in patients with HR-positive/HER2-negative early breast cancer. Dennis Slamon is the first author listed in the official programme (Slamon et al., 2026).

This is an important stage in the maturation of the NATALEE dataset. In HR-positive early breast cancer, where recurrence risk can persist for many years, longer follow-up is essential for understanding whether an adjuvant intervention produces durable benefit beyond the period of active treatment.

The six-year analysis should therefore help define the persistence of efficacy and, most importantly, provide a more mature assessment of overall survival.

PANKU-Breast01: Phase III Data in Previously Treated HR-Positive/HER2-Negative Disease

LBA50 — PANKU-Breast01 is a randomized phase III study of izalontamab brengitecan in previously treated unresectable locally advanced or metastatic HR-positive/HER2-negative breast cancer. Bo Lan is listed as first author (Lan et al., 2026).

The study enters a setting in which treatment sequencing has become increasingly complicated. Patients with HR-positive/HER2-negative metastatic disease may now receive several endocrine-based and targeted therapies before later-line systemic treatment, creating a need for effective strategies after multiple prior exposures. PANKU-Breast01 is therefore one of the late-breaking studies to watch for its potential contribution to the treatment pathway after established endocrine and targeted approaches.

KEYNOTE-B49: Testing Pembrolizumab in HR-Positive/HER2-Negative Advanced Breast Cancer

LBA51 — KEYNOTE-B49 is a randomized, double-blind phase III study evaluating pembrolizumab versus placebo in combination with chemotherapy in HR-positive/HER2-negative advanced breast cancer. Hope Rugo is listed as the first author (Rugo et al., 2026).

The trial addresses an important question about the possible extension of immunotherapy into a breast cancer subtype where checkpoint inhibition has not had the same established role as in triple-negative disease. Because the study compares chemotherapy with or without pembrolizumab, the ESMO presentation will be important for determining whether the addition of immune checkpoint blockade produces clinically meaningful benefit in this advanced HR-positive/HER2-negative population.

If positive, the clinical interpretation will likely depend heavily on the magnitude of benefit and whether any biomarker-defined population can be identified. If negative, it would further emphasize the difficulty of extending immunotherapy across breast cancer subtypes without more precise biological selection.

FINER: Overall Survival With Fulvestrant and Ipatasertib

LBA14 — FINER, formally the CCTG/BCT MA.40 study, will report overall survival results from a randomized phase III trial of fulvestrant plus ipatasertib in HER2-negative, ER-positive metastatic breast cancer. Andrew Redfern is listed as first author (Redfern et al., 2026).

The fact that ESMO 2026 will present an OS analysis makes this study particularly relevant. In metastatic HR-positive disease, where multiple treatments may be given sequentially, establishing an overall survival effect can be considerably more difficult than demonstrating improvement in disease control.

FINER should therefore help clarify the longer-term clinical value of this endocrine-targeted combination and its potential place within an increasingly crowded treatment sequence.

VIKTORIA-1: Updated Phase III Results After Endocrine Resistance

LBA16 — VIKTORIA-1 will provide updated results from a randomized phase III study of gedatolisib plus fulvestrant, with or without palbociclib, versus standard of care in HR-positive/HER2-negative advanced breast cancer. Barbara Pistilli is listed as first author (Pistilli et al., 2026).

The study sits directly within one of the most difficult areas of current breast oncology: treatment after progression through endocrine therapy and CDK4/6 inhibition.

Its design is particularly informative because it evaluates gedatolisib with fulvestrant both with and without continued CDK4/6 inhibition. The updated analysis may therefore contribute to the broader question of whether cell-cycle inhibition should be retained in selected patients after progression or whether treatment should shift completely toward another pathway-directed strategy.

evERA Breast Cancer: Moving From Efficacy Toward Biomarker Selection

2RO — evERA Breast Cancer will present retrospective exploratory biomarker analyses from the phase III study of giredestrant plus everolimus in ER-positive/HER2-negative advanced breast cancer after CDK4/6 inhibitor therapy. Sara Tolaney is listed as first author (Tolaney et al., 2026).

Unlike several other presentations in this watchlist, the primary purpose of this ESMO update is not another conventional efficacy analysis. It is an attempt to understand which biological characteristics may be associated with treatment response.

That makes evERA particularly relevant to the evolution of post-CDK4/6 treatment. As the number of available endocrine and targeted therapies increases, treatment selection will increasingly depend on identifying the biology driving resistance rather than applying the same sequence to every patient.

The exploratory nature of the analysis should remain central to interpretation, but biomarker findings could generate hypotheses for more individualized treatment selection.

postMONARCH: Overall Survival After Prior CDK4/6 Inhibition

1RO — postMONARCH will report overall survival from the phase III trial of abemaciclib plus fulvestrant versus placebo plus fulvestrant after progression on a previous CDK4/6 inhibitor plus endocrine therapy. Kevin Kalinsky is listed as first author (Kalinsky et al., 2026).

The central clinical question is highly practical: after progression on one CDK4/6-based regimen, can continued inhibition of the same pathway with abemaciclib and a new endocrine partner translate into a meaningful survival advantage?

This is increasingly relevant because post-CDK4/6 treatment is no longer a single linear sequence. Clinicians must choose between additional endocrine-based therapy, pathway-directed treatment, ADCs, and chemotherapy according to tumor biology and prior treatment.

An OS analysis therefore has the potential to clarify whether continued CDK4/6 inhibition provides benefit that extends beyond delaying progression.

OptiTROP-Breast01: Final Overall Survival in Previously Treated TNBC

4639RO — OptiTROP-Breast01 will report the final overall survival analysis of sacituzumab tirumotecan versus chemotherapy in previously treated locally recurrent or metastatic triple-negative breast cancer. Ying Fan is the first author listed in the programme (Fan et al., 2026).

The final OS analysis is particularly important in a TNBC landscape increasingly shaped by ADCs. As more agents targeting overlapping antigens or using related payload classes become available, mature survival data will become central to defining treatment sequence rather than simply establishing antitumor activity.

OptiTROP-Breast01 will therefore be important both as an efficacy readout and as part of the larger discussion about where different ADCs should be positioned across the metastatic treatment pathway.

Importantly, the official programme identifies this abstract as 4639RO, correcting the 3RO designation shown in some unofficial summaries.

SWITCH: Directly Testing ADC Sequencing After Prior ADC Therapy

4RO — SWITCH may be one of the most conceptually important studies in the programme because it directly addresses what happens after an ADC has already been used. The prospective, open-label phase II platform trial evaluates target switching with conserved-payload novel ADCs in patients with metastatic breast cancer following previous ADC therapy (Liu et al., 2026).

This question is becoming increasingly important as ADC exposure moves earlier in metastatic disease and into curative-intent treatment. Sequencing cannot be understood solely by the surface target. Resistance may involve the antigen, internalization, trafficking, linker characteristics, payload sensitivity, drug efflux, or several mechanisms simultaneously. SWITCH is notable because its title explicitly tests a strategy in which the target changes while the payload is conserved.

That makes the study relevant well beyond any individual ADC. It may contribute to a larger framework for understanding whether changing the target is sufficient after ADC progression or whether future sequencing will also need to change the cytotoxic payload mechanism.

A Programme Increasingly Defined by Treatment Sequence

Taken together, these ten presentations illustrate how the central questions in breast oncology are changing. In early disease, TALENT examines whether an ADC can be integrated into neoadjuvant treatment for HER2-low disease, while NATALEE asks whether the benefit of adjuvant CDK4/6 inhibition remains durable as overall survival follow-up matures.

In advanced HR-positive/HER2-negative disease, the programme is heavily focused on what happens after established endocrine-based therapy. KEYNOTE-B49, FINER, VIKTORIA-1, evERA, and postMONARCH approach that problem through immunotherapy, pathway-directed treatment, continued CDK4/6 inhibition, and biomarker-guided interpretation.

The ADC field is evolving just as quickly. PANKU-Breast01 evaluates another ADC strategy in previously treated HR-positive disease, OptiTROP-Breast01 reaches final OS in TNBC, and SWITCH moves directly into the emerging problem of post-ADC treatment.

The common theme is therefore less about identifying one new active drug and more about building a rational treatment architecture.

The Bottom Line

The ESMO 2026 breast cancer programme reflects a field moving toward more mature survival endpoints and increasingly complex sequencing decisions. Several studies could provide long-awaited survival information: NATALEE at six years, FINER with OS, postMONARCH with OS, and OptiTROP-Breast01 with final OS.

Others address emerging therapeutic territory: TALENT in HER2-low early breast cancer, KEYNOTE-B49 in HR-positive advanced disease, VIKTORIA-1 and evERA after CDK4/6 inhibition, PANKU-Breast01 in previously treated HR-positive disease, and SWITCH after prior ADC exposure.

The results will ultimately determine how much these studies alter practice. But even before presentation, the official programme makes one direction clear: the future of breast cancer treatment is increasingly about choosing not only the right therapy, but the right sequence for each stage of the disease.

References

1. Hurvitz, S., et al. (2026). Final results of TALENT: A neoadjuvant trial of T-DXd with or without anastrozole, or in sequence with chemotherapy for HER2-low, HR+ early-stage breast cancer [Late-breaking abstract LBA23]. ESMO Congress 2026.
2. Slamon, D., et al. (2026). Adjuvant ribociclib plus nonsteroidal aromatase inhibitor in patients with HR+/HER2− early breast cancer: NATALEE 6-year overall survival and efficacy outcomes [Late-breaking abstract LBA25]. ESMO Congress 2026.
3. Lan, B., et al. (2026). PANKU-Breast01: Randomized phase III study of izalontamab brengitecan in previously treated unresectable locally advanced or metastatic HR+/HER2− breast cancer [Late-breaking abstract LBA50]. ESMO Congress 2026.
4. Rugo, H., et al. (2026). Results from KEYNOTE-B49: A phase III randomized double-blind study of pembrolizumab versus placebo plus chemotherapy in HR+/HER2− advanced breast cancer [Late-breaking abstract LBA51]. ESMO Congress 2026.
5. Redfern, A., et al. (2026). Fulvestrant and ipatasertib for HER2-negative, ER-positive metastatic breast cancer: Overall survival results of the CCTG/BCT MA.40/FINER study [Late-breaking abstract LBA14]. ESMO Congress 2026.
6. Pistilli, B., et al. (2026). VIKTORIA-1: Updated results of gedatolisib plus fulvestrant ± palbociclib versus standard of care in HR+/HER2− advanced breast cancer [Late-breaking abstract LBA16]. ESMO Congress 2026.
7. Tolaney, S., et al. (2026). Retrospective exploratory biomarker analyses from evERA Breast Cancer: Giredestrant plus everolimus after CDK4/6 inhibitor therapy [Rapid oral abstract 2RO]. ESMO Congress 2026.
8. Kalinsky, K., et al. (2026). Overall survival from the phase III postMONARCH trial of abemaciclib plus fulvestrant versus placebo plus fulvestrant after prior CDK4/6 inhibitor plus endocrine therapy [Rapid oral abstract 1RO]. ESMO Congress 2026.
9. Fan, Y., et al. (2026). Final overall survival analysis of sacituzumab tirumotecan versus chemotherapy in previously treated locally recurrent or metastatic triple-negative breast cancer: Phase III OptiTROP-Breast01 [Rapid oral abstract 4639RO]. ESMO Congress 2026.
10. Liu, X., et al. (2026). Target switching with conserved-payload novel ADCs in patients with metastatic breast cancer following prior ADC therapy (SWITCH): A prospective, open-label, phase II platform trial [Rapid oral abstract 4RO]. ESMO Congress 2026.