TKIs and beyond
In addition to ADCs, TKIs continue to make their mark in the targeted HER2 therapeutic space. The approvals of tucatinib and neratinib last year represented an important advance in treating HER2-positive MBC, particularly for patients with brain metastases. The HER2CLIMB trial, for instance, found that tucatinib combined with trastuzumab and capecitabine had a 4.5-month overall survival advantage compared with placebo (21.9 vs 17.4) and a median progression-free survival advantage of 5.4 months in patients with active brain metastases (9.5 vs 4.1) and 8.3 months in patients with stable metastases (13.9 vs 5.6).
Given this progress, experts are looking to add new TKIs to the armamentarium. In particular, pyrotinib — already approved in China for treating HER2-positive MBC — has demonstrated significantly longer progression-free survival compared with a standard TKI, lapatinib. The phase 3 PHOEBE trial results, published in The Lancet in early 2021, found a median progression-free survival of 12.5 months in patients randomly assigned to receive pyrotinib plus capecitabine compared with 6.8 months in those receiving lapatinib plus capecitabine. The investigators also reported “manageable toxicity”; diarrhea was the most common grade 3 adverse event, occurring in 31% of the pyrotinib group vs. 8% of the lapatinib group, and overall serious adverse events occurred in 10% of patients receiving pyrotinib vs. 8% of those receiving lapatinib.
More recent data on pyrotinib come from the phase 2 PERMEATE trial, which focused on the safety and efficacy of the agent in patients with advanced disease and brain metastases. The investigators, who presented their findings at the 2021 virtual ASCO meeting (abstract 1037), reported that radiation therapy–naive patients receiving pyrotinib plus capecitabine had an overall response rate of 74.6% in the central nervous system. Patients experiencing progression after whole-brain or stereotactic radiation therapy, however, had a comparatively lower overall response rate of 42.1%.
Similarly, median progression-free survival was much higher in the radiation therapy–naive patients (12.1 vs 5.6 months in the radiation therapy cohort). Similar to the PHOEBE trial, the most common grade 3 adverse event was diarrhea (23.1%), followed by decreased neutrophil and white blood cell counts (12.8% for both), anemia (9%), and hand-foot syndrome (7.7%). The main question for Dr. Kalinsky is how well pyrotinib will ultimately stack up to tucatinib and neratinib. “Pyrotinib — like neratinib — was shown to be superior to lapatinib plus capecitabine , but its role may be limited by its gastrointestinal toxicity,” he said. In addition to research focused on expanding the selection of novel ADCs and TKIs, researchers are also exploring new combinations of approved treatments and whether these combinations can be used earlier in treatment sequencing.
Take the CompassHER2 trials. The ongoing phase 3 trial in patients with high-risk HER2-positive breast cancer and residual disease will explore whether tucatinib plus T-DM1 compared with T-DM1 alone improves overall survival and recurrence-free survival and prevents brain metastases. Another possibility currently under investigation is pairing tucatinib and trastuzumab deruxtecan, instead of T-DM1. “Overall, it’s exciting that we are increasing the number of therapeutic options and combinations,” commented Debu Tripathy, MD, professor and chairman in the department of breast medical oncology at the University of Texas MD Anderson Cancer Center in Houston. “Having more choices allows us to tailor therapies to manage resistance and prolong patients’ responses.”
Curbing brain metastasis, according to Dr. Brufksy, is particularly important, and experts need to explore the extent to which ADCs can penetrate the blood-brain barrier. Already, a subgroup analysis of the DESTINY-Breast01 trial found that trastuzumab deruxtecan appeared to be active in patients with brain metastases. Investigators reported an overall response rate of 58.3% and a median progression-free survival of 18.1 months — results in line with those in the general study cohort — but the study population did not include patients with untreated or progressive brain metastases. A phase 2 study currently under way will examine whether patients with HER2-positive and HER2-low breast cancer who have untreated or progressive brain metastases respond to trastuzumab deruxtecan as well. Ultimately, Dr. Brufksy hopes the recent successes with preventing brain metastases in pediatric acute lymphoblastic leukemia (ALL) foreshadow what›s to come in HER2-positive MBC.
“When we figured out how to treat brain metastases prophylactically in childhood ALL, we saw a huge improvement in the cure rate, which is ultimately my vision for HER2-positive disease,” Dr. Brufsky remarked. “Are there cures for HER2-positive MBC on the horizon? We don’t know yet, but the field has really exploded in recent years.”
A version of this article first appeared on Medscape.com.