Phase 3 Breast Cancer Trial Data Highlights from Q1 2026

Breast cancer research advanced significantly in early 2026 with multiple phase 3 clinical trial datasets emerging that may influence clinical practice. Key findings include positive results for several novel therapies across different breast cancer subtypes, with detailed data expected at upcoming medical meetings.

The BL-B01D1-307 trial investigated izalontamab brengitecan (iza-bren), a HER3- and EGFR-directed bispecific antibody-drug conjugate, in adult patients with unresectable, locally advanced or metastatic triple-negative breast cancer who had received 1 or 2 prior lines of chemotherapy in the locally advanced or metastatic settings, as well as a prior taxane. Patients in the iza-bren arm received the ADC intravenously for one 3-week cycle; patients who achieved clinical benefit from the agent could continue treatment for additional cycles until disease progression, intolerable toxicity, or other reasons. Patients in the chemotherapy arm received physician's choice of eribulin, vinorelbine, gemcitabine, or capecitabine on the same schedule as the iza-bren arm.

The persevERA trial evaluated giredestrant plus palbociclib (Ibrance) in estrogen receptor-positive, HER2-negative locally advanced or metastatic breast cancer that was not amenable to curative-intent therapy. Patients were randomly assigned 1:1 to receive either giredestrant once daily, palbociclib at 125 mg on days 1 to 21 of each 28-day cycle, and a letrozole-matched placebo once daily; or a giredestrant-matched placebo once daily, letrozole once daily, and palbociclib at the same dose and schedule as the investigational arm.

An analysis of the phase 3 PATINA trial published in January 2026 in The New England Journal of Medicine examined palbociclib in HR-positive, HER2-positive advanced breast cancer. At a median follow-up of 53.5 months, the median progression-free survival in the palbociclib group was 44.3 months versus 29.1 months in the standard-of-care group. The confirmed overall response rate was 32.9% in the palbociclib arm versus 24.8% in the control arm. At the data cutoff, 60 and 63 patients in these respective arms had died. Per the trial protocol, the final overall survival analysis will be conducted after 247 deaths have occurred.

Patients in the PATINA trial were randomly assigned 1:1 to receive maintenance therapy with HER2-targeted and endocrine therapies with or without palbociclib. Endocrine therapies included fulvestrant or an aromatase inhibitor, and premenopausal patients were also required to receive ovarian suppression. Palbociclib was given at 125 mg daily for the first 21 days of each 28-day cycle. Investigator-assessed progression-free survival served as the primary end point, with secondary end points including confirmed overall response rate, overall survival, and safety.

Trial investigators noted that the addition of palbociclib was associated with increased toxic effects. Common grade 3 or higher adverse effects seen in the palbociclib versus control groups, respectively, were neutropenia (60.5%; 2.0%) and leukopenia (16.1%; 0.8%).

Another trial evaluated first-line sacituzumab govitecan-hziy plus pembrolizumab in metastatic triple-negative breast cancer. This trial enrolled adult patients with locally advanced unresectable or metastatic triple-negative breast cancer who had not been previously treated for advanced disease and who had PD-L1-positive disease. Patients were randomly assigned 1:1 to receive either sacituzumab govitecan at 10 mg/kg on days 1 and 8 in combination with pembrolizumab at 200 mg on day 1 of each 21-day cycle, or physician's choice of paclitaxel, nab-paclitaxel, or gemcitabine plus carboplatin in combination with pembrolizumab at the same dose and schedule as in the investigational arm. The investigators noted that the safety profile of sacituzumab govitecan plus pembrolizumab was consistent with those of the individual drugs.