SAN ANTONIO – (PFS) versus T-DM1 alone, according to results from the phase III HER2CLIMB-02 study. A subanalysis of patients with brain metastases at baseline also showed an improvement in this population.
Brain metastases are common HER2+ breast cancer, and this is associated with poor outcomes, according to Sara A. Hurvitz, MD, who presented the study at the San Antonio Breast Cancer Symposium. There are few treatment options available for this population.
“Adding tucatinib to TDM-1 significantly improved progression free survival in patients with previously treated HER2+ advanced disease. The types of adverse events were consistent with previous reporting, and this is the second randomized study which included patients with brain metastases to demonstrate that a tucatinib-based regimen delays disease progression in this disease setting,” said Dr. Hurvitz, professor and head of the division of hematology and oncology at the University of Washington Department of Medicine and senior vice president and director of the Clinical Research Division at Fred Hutchinson Cancer Center.
Both tucatinib and TDM-1 target the HER2 receptor. T-DM1 is an antibody-drug conjugate (ADC) of trastuzumab (Herceptin) and the drug emtansine that has received FDA approval as monotherapy for both early- and late-stage HER2-positive breast cancer. Tucatinib is a small-molecule HER2 inhibitor and has efficacy against disease progression in the central nervous system, which is unusual among HER2-targeted therapies.
The earlier HER2CLIMB trial showed improved outcomes among heavily pretreated patients — including those with brain metastases — when tucatinib was added to trastuzumab and capecitabine (Xeloda, Genentech). In 2020, the FDA approved the combination for advanced unresectable or metastatic HER2-positive breast cancer, including brain metastases.
To determine if tucatinib could also improve responses when combined with a trastuzumab-based ADC, the researchers randomized 463 patients to tucatinib plus T-DM1 or placebo plus T-DM1. Nearly half (44.1%) of patients had brain metastases at baseline. Over a median follow-up of 24.4 months, the combination group had a 24% lower risk of progression or death (hazard ratio [HR], 0.76; P = .0163) and a longer median progression-free survival (9.5 months versus 7.4 months).
The PFS benefit was also seen in patients with baseline brain metastases (HR, 0.64; 95% CI, 0.46-0.89]). An insufficient number of survival events had occurred at the interim analysis to determine OS at the time of the presentation.
There was no statistically significant difference in overall response rate in the intervention arm. Treatment-emergent adverse events (TEAEs) that were more common in the tucatinib arm included nausea (65.4% vs. 49.4%), diarrhea (56.7% vs. 26.6%), and fatigue (48.9% vs. 37.3%). Grade 3 or higher TEAEs in the tucatinib arm included alanine and aspartate aminotransferase elevations (16.5% for both), versus 2.6% in the control arm for both. TEAEs associated treatment discontinuation occurred among 22.1% in the tucatinib arm and 11.6% in the control arm. TEAEs that led to mortality occurred in 1.3% of the tucatinib group and 0.9% of the control arm.
“I think tucatinib really does contain level one evidence for use in the setting of CNS metastases. There’s not yet data that has replaced that, so I will continue to consider using it in the second line setting, as it’s currently indicated in the presence of brain metastases. Without brain metastases, based on [the DESTINY-Breast03 trial], I’d probably opt for [trastuzumab deroxtecan], which is still the standard,” said Dr. Hurvitz.
Following the talk, Valentina Guarneri, MD, PhD, served as a discussant. She underscored the clinical need for treatment of patients with brain metastases.
“Brain metastases represent a devastating event for our patients and remain an unmet need considering that all of these patients will eventually require local therapies, with potentially debilitating sequelae. Since optimal therapy for these patients should not be an afterthought, clinical trials taking the risk of including these patients must be valued,” said Dr. Guarneri, professor of oncology at the University of Padua in Italy.
She acknowledged the success of the dual HER2 inhibitor strategy, and said it opens up avenues for combinations with novel antibody-drug conjugates. “HER2CLIMB-02 is unlikely to change the current algorithm, but it reinforces the role of tucatinib in the treatment of HER2+ metastatic breast cancer. The data further support studies in the early disease setting aiming to prevent the development of brain metastases,” said Dr. Guarneri.
The study was funded by Seagen. Dr. Hurvitz has received research funding from Ambrx, Arvinas, AstraZeneca, Bayer, Celcuity, CytomX Therapeutics, Daiichi Sankyo, Dantari Inc., Dignitana, Genentech, (Roche), G1 Therapeutics, Gilead Sciences Inc., Greenwich LifeSciences Inc., GSK, Immunomedics, Eli Lilly and Company, Loxo Oncology, MacroGenics, Novartis, OBI Pharma Inc., Orinove Inc., Orum Therapeutics, Pfizer, Phoenix Molecular Designs, Pieris Pharmaceuticals Inc., Puma Biotechnology, Radius Health, Sanofi, Seagen, and Zymeworks; has received royalties from McGraw Hill, Sage Publications, Wiley, and Wolters Kluwer; has served on the data and safety monitoring board for Alliance Foundation Trials LLC, Atossa Therapeutics, and the Quantum Leap Healthcare Collaborative; and has received honoraria from the Vaniam Group and OncLive. Her husband holds stock in ROMTech. Dr. Guarneri has been a member of the advisory boards for AstraZeneca, Daiichi Sankyo, Eisai, Eli Lilly, Exact Sciences, Gilead, Merck Serono, MSD, Novartis, Pfizer, Olema Oncology, and Pierre Fabre. She has been an invited speaker for AstraZeneca, Daiichi Sankyo, Eli Lilly, Exact Sciences, Gilead, GSK Novartis, and Zentiva.