Zanidatamab Combo Appears ‘Exciting’ in HER2+/HR+ Metastatic Breast Cancer

Adding zanidatamab to palbociclib (Ibrance) and fulvestrant (Faslodex) produced “exceptional” results with respect to progression-free survival (PFS) among pretreated patients with HER2-positive, hormone receptor (HR)–positive, metastatic breast cancer, according to Sara Hurvitz, MD, FACP.

In a conversation with CancerNetwork^®, Hurvitz, senior vice president, director, and professor of the Clinical Research Division at Fred Hutch Cancer Center, spoke about findings from a phase 2a trial (NCT04224272) evaluating the zanidatamab-based regimen among those with HR-positive, HER2-positive disease. The combination yielded a median PFS of 12 months in the overall population, and 67% of patients were progression free at 6 months. Additionally, the confirmed objective response rate among those with centrally confirmed HER2-positive disease was 48% (95% CI, 29%-68%), which included complete responses in 10% and partial responses in 38%.

Hurvitz also stated that the experimental combination yielded a positive safety profile. Overall, 67% of patients experienced grade 3/4 treatment-related adverse effects, which commonly included neutrophil count decreases or neutropenia (53%), diarrhea (14%), and anemia (10%).

Investigators presented these findings at the 2023 San Antonio Breast Cancer Symposium (SABCS).

Transcript:

Zanidatamab is a really interesting molecule. It’s actually a bispecific or biparatopic antibody that binds 2 different non-overlapping extracellular domains on HER2. Binding these 2 domains can lead to cross linking, clustering, and internalization of HER2. It has shown some pretty interesting results in the preclinical and early phase clinical setting. At SABCS, the results of a phase 2a study looking at zanidatamab in combination with palbociclib and fulvestrant were presented.

The PFS6 was 67%, meaning at 6 months, 67% of the patients had not yet experienced a progression event. The median [PFS] overall was 12 months. If you just looked at the patients who had centrally confirmed HER2-positive disease, it was 15 months. These are exceptional results in a patient population that is so heavily pretreated. Of course, only [patients with] hormone receptor–positive, HER2-positive breast cancer were enrolled in this study, and that’s the subset of patients who were really being evaluated. The objective response rate was 48% in patients who had centrally confirmed HER2-positive disease.

These results are pretty exciting; the toxicity profile is really quite good. The rates of grade 3/4 events outside of the neutropenia—which is associated with palbociclib—were fairly uncommon. I’m excited to see further results of this in a later-stage study.

Reference

Escrivá-de-Romani S, Cejalvo JM, Alba E, et al. Primary results from a phase 2a study of zanidatamab (zani) + palbociclib (palbo) + fulvestrant (fulv) in HER2+/HR+ metastatic breast cancer (mBC). Presented at the 2023 San Antonio Breast Cancer Symposium; December 5-9, 2023; San Antonio, TX; abstract LBO1-04.