SABCS 2023: Bispecific Antibody Plus Palbociclib and Fulvestrant in Metastatic Breast Cancer

By: Julia Fiederlein Cipriano, MS
Posted: Friday, December 15, 2023

Treatment with the HER2-targeted bispecific antibody zanidatamab plus the CDK4/6 inhibitor palbociclib and the estrogen receptor antagonist fulvestrant seemed to confer “promising” progression-free survival outcomes and “durable” responses in heavily pretreated patients with unresectable locally advanced or metastatic HER2-positive, hormone receptor–positive breast cancer, according to Santiago Escrivá-de-Romaní, MD, of Vall d’Hebron University Hospital, Barcelona, and colleagues. The primary results of a phase IIa study, which were presented during the 2023 San Antonio Breast Cancer Symposium (SABCS; Abstract LBO1-04), also revealed a manageable safety profile.

“These results support further development of a novel chemotherapy-free treatment regimen,” the investigators concluded.

A total of 51 patients with an Eastern Cooperative Oncology Group performance status of up to 1 who previously received trastuzumab, pertuzumab, and ado-trastuzumab emtansine (T-DM1) were treated with zanidatamab plus palbociclib and fulvestrant. Follow-up data were provided for a median of 16.1 months.

At 6 months, the progression-free survival rate was 67% in all patients and 69% in those with centrally confirmed HER2-positive disease. The median durations of progression-free survival were 11.7 and 14.9 months, respectively. Patients with PAM50-confirmed luminal B (n = 12) vs HER2-enriched (n = 16) disease were found to experience a numerically longer median duration of progression-free survival (11.7 vs 9.3 months; P = .74) and comparable 6-month rates (66.7% vs 62.5%).

The most frequently reported treatment-related adverse events with the combination therapy were diarrhea (80%), decreased neutrophil count/neutropenia (59%), nausea (39%), stomatitis (37%), anemia (29%), vomiting (25%), and asthenia (24%). Treatment-related adverse events of grade 3 or higher were observed in at least two patients included decreased neutrophil count/neutropenia (53%), diarrhea (14%), anemia (10%), thrombocytopenia (6%), hypokalemia (4%), and hypomagnesemia (4%). The investigators reported one serious treatment-related adverse event. Cardiac events (n = 6) and infusion-related reactions (n = 2) were adverse events of special interest. No treatment-related deaths were documented.

Disclosure: For full disclosures of the study authors, visit sabcs.org.

2023 San Antonio Breast Cancer Symposium

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