A drug revived by researchers at The University of Texas MD Anderson Cancer Center, Houston, continues to provide high response rates among stage IV non-small cell lung cancer (NSCLC) patients with genetic mutations that have routinely defeated treatment.
Early results from a phase II clinical trial, reported in an abstract released for the 2018 IASLC World Conference on Lung Cancer, show 23 of 40 patients (58%) with exon 20 mutations in the EGFR and six of 12 patients (50%) with exon 20 mutations in HER2 had their tumors shrink at 8 weeks after treatment with poziotinib.
"These clinical trial results so far show poziotinib is likely the first real advance for patients with EGFR and HER2 exon 20 mutations, for whom no available targeted therapies have been effective," said principal investigator John Heymach, MD, PhD, Professor and Chair of Thoracic/Head and Neck Medical Oncology.
Previous early results had been reported for the EGFR patients, the IASLC presentation is the first to include HER2 patients. Researchers estimate exon 20 EGFR mutations occur in about 1 percent of NSCLC patients and HER2 exon 20 variations occur in about 3 percent.
The MD Anderson investigator-initiated clinical trial provides the largest dataset among exon 20 lung cancer patients worldwide. A multi-center phase II trial of poziotinib has been opened as well.
Response rates of exon 20 patients to other targeted therapies aimed at EGFR and HER2 have been 12 percent or less, the researchers noted. Median progression-free survival on the EGFR arm of the poziotinib trial was 5.6 months. It has not been reached in the HER2 arm, which opened later. Disease control rate-total of complete responses, partial responses, and stable disease-was 90 percent for the EGFR patients and 83 percent for the HER2 patients.
In the EGFR cohort, 60 percent of patients had a side effect of grade 3 or higher, most commonly skin rash (27.5%), diarrhea (12.5%), and paronychia (7.5%); one patient stopped treatment due to grade 3 skin rash. Side effects in the EGFR cohort were similar. One death from pneumonitis in the HER2 cohort was considered to be possibly drug-related.
Resurrecting Poziotinib
Heymach's team decided to focus on exon 20 patients while selecting projects for the Lung Cancer Moon Shot, part of MD Anderson's Moon Shots Program, a collaborative effort to accelerate the development of scientific discoveries into life-saving advances. Review of a patient database found exon 20 patients had a median progression-free survival of just 2 months.
In a series of cell line and mouse model experiments combined with structural modeling of both target EGFR and HER2 mutations and available drugs to hit them, the researchers found that poziotinib's structure made it a good fit for exon 20-mutated disease, even though it had largely failed against other mutations. The tighter target pocket on EGFR and HER2 tumors with exon 20 mutations also explained why other targeted therapies had been unable to bind with and inhibit the proteins.