Oral abstract session: early breast cancer

For this highlight video, Prof Dr François Duhoux, medical oncologist at Cliniques Universitaires Saint-Luc in Brussels, selected a series of abstracts presented during the oral session on early breast cancer at ASCO 2026. The selection features studies addressing treatment de-escalation, endocrine therapy optimization, immunotherapy, HER2-positive disease, and surgical management.

Arguably one of the most clinically relevant presentations concerned the OPTIMA trial, a de-escalation study evaluating the use of gene expression profiling to guide adjuvant chemotherapy decisions in patients with hormone receptor-positive (HR+), HER2-negative (HER2-) early breast cancer. While assays such as Oncotype DX and MammaPrint are already established tools in this setting, Optima investigated the Prosigna assay based on the PAM50 gene signature. Patients older than 40 years with clinical characteristics that would normally indicate chemotherapy were randomized either to standard chemotherapy or to a strategy incorporating genomic profiling. Patients with a high-risk Prosigna score received chemotherapy followed by endocrine therapy, whereas those with a low-risk score were treated without chemotherapy. The study was designed as a non-inferiority trial and met its primary objective. Among patients classified as low risk by Prosigna, omission of chemotherapy was associated with excellent outcomes. At a median follow-up of four years, distant relapse-free survival reached 96% in patients who avoided chemotherapy based on the genomic test, compared with 97% in patients managed with standard chemotherapy. The findings were consistent across premenopausal and postmenopausal populations and remained valid in patients with a higher nodal burden, including those with up to nine positive lymph nodes.¹

An updated analysis from the NATALEE trial explored whether baseline gene expression profiles could identify subgroups deriving greater benefit from the addition of ribociclib to adjuvant endocrine therapy. The analyses suggested that patients with certain PAM50 molecular subtypes, higher genomic risk scores, or more proliferative tumors may experience greater benefit from ribociclib. Nevertheless, the observed differences were not considered sufficiently robust to alter current clinical practice. The results therefore provide biological insights into treatment response without establishing new biomarkers for patient selection in routine care.²

Further attention was given to subgroup analyses from the phase III lidERA trial evaluating adjuvant giredestrant in patients with high-risk HR+/HER2- early breast cancer. Previous presentations had demonstrated positive outcomes with this oral selective estrogen receptor degrader (SERD), but uncertainty remained regarding the consistency of benefit across menopausal status. The ASCO 2026 analysis removed this uncertainty and showed significant benefit for giredestrant in both pre- and postmenopausal patients.³

Long-term outcomes from KEYNOTE-522 were also presented. This landmark study evaluated the addition of pembrolizumab to neoadjuvant chemotherapy in early-stage triple-negative breast cancer (TNBC). With almost eight years of follow-up now available, the updated analysis confirmed sustained benefits across multiple clinically relevant endpoints. Event-free survival, overall survival, and distant relapse-free survival all continued to favor the pembrolizumab-containing regimen. The safety profile remained consistent with previous reports, suggesting that immune-related toxicities largely occur early during treatment and do not continue to accumulate over time. These findings further characterize the durability of benefit observed with immune checkpoint inhibition in the curative setting.⁴

Among the HER2-positive studies, the Chinese Neo-Healer trial evaluated a novel neoadjuvant strategy incorporating two investigational agents. The regimen combined anbenitamab, a HER2-targeting antibody capable of binding two distinct HER2 epitopes, with a novel albumin-bound docetaxel formulation, administered with or without carboplatin. This experimental combination was compared with the established THP regimen, again with or without carboplatin. The study reported higher pathological complete response rates with the investigational approach, suggesting enhanced antitumor activity in the neoadjuvant setting.⁵

Another Chinese phase III study addressed a more specific clinical question in HR+/HER2- breast cancer. The trial enrolled patients who had residual disease following standard neoadjuvant chemotherapy and evaluated the role of additional adjuvant chemotherapy. The principal finding was that patients who had received anthracycline-based neoadjuvant treatment appeared to derive an overall survival (OS) benefit from subsequent taxane administration. Because treatment sequencing and standards differ substantially from contemporary European practice, the applicability of these results to Belgian patients was considered limited. Nevertheless, the study contributes to the broader discussion regarding treatment escalation in patients with residual disease after neoadjuvant therapy.⁶

The oral session also included important updates in locoregional management. The SENOMAC trial investigated whether completion axillary lymph node dissection can be safely omitted in patients with one or two macrometastatic sentinel lymph nodes. Previous studies had shown that completion dissection frequently identifies additional positive nodes, but definitive overall survival data had been lacking. The newly presented five-year analysis demonstrated non-inferiority for omission of axillary dissection. OS was very similar between treatment strategies, with only a 1% absolute difference observed. These findings add further evidence supporting less extensive axillary surgery in appropriately selected patients while avoiding the morbidity associated with full axillary dissection.⁷

The AXSANA study focused on identifying biomarkers associated with pCR following neoadjuvant chemotherapy. The analysis reinforced the importance of tumor biology over initial anatomical stage in predicting treatment response. An additional observation concerned post-treatment nodal assessment. Among patients who were clinically considered to have persistent axillary involvement after neoadjuvant chemotherapy, approximately one-third were ultimately found to have no residual nodal disease at surgery. This discrepancy highlights the limitations of clinical assessment following systemic treatment and may have implications for future de-escalation strategies in axillary management.⁸

Finally, a study conducted by plastic surgeons examined breast reconstruction techniques after mastectomy, comparing prepectoral versus subpectoral implant placement. Patients receiving prepectoral reconstruction reported better quality-of-life outcomes than those undergoing the traditional subpectoral approach. However, this advantage was accompanied by a higher frequency of implant replacement procedures over time. The findings illustrate the balance between patient-reported outcomes and long-term surgical durability that continues to influence reconstructive decision-making in breast cancer care.⁹