The investigational anti-body drug conjugate (ADC) resistant to endocrine therapy, data from the phase 3 TROPION-Breast01 trial showed.
At a median follow-up of 10.8 months, the median progression-free survival (PFS) was 6.9 months for patients randomly assigned to receive Dato-DXd, compared with 4.9 months for the investigator’s choice of chemotherapy with either eribulin mesylate, vinorelbine, capecitabine, or gemcitabine. This difference translated into a 37% reduction in risk of disease progression with the ADC, reported Aditya Bardia, MD, MPH, director of the breast cancer research program at the Mass General Cancer Center in Boston.
Patients who received Dato-DXd had less than half the number of grade 3 or greater toxicities and fewer dose reductions or interruptions than patients who received chemotherapy, he noted in an oral abstract session at the 2023 European Society for Medical Oncology Congress.
“Overall, results support Dato-DXd as a potential new therapeutic option for patients with metastatic hormone receptor–positive breast cancer,” he said.
Different ADC, same target
Dr. Bardia noted that there is an unmet need for effective therapies for patients with metastatic HR+/HER2– breast cancer who experience disease progression after endocrine therapy and at least one line of systemic therapy.
Although chemotherapy is widely used in this population, it’s associated with low response rates, poor prognosis, and significant toxicities, including hematologic and neurologic adverse events (AEs).
Dato-DXd is composed of a monoclonal antibody targeting TROP2, a transmembrane glycoprotein overexpressed in cancer cells, linked to the topoisomerase 1 inhibitor deruxtecan as the toxic payload.
Dr. Bardia explained that Dato-DXd has four properties that distinguish it from other TROP2-directed ADCs: an optimized drug to antibody ratio of 4, a stable linker-payload, tumor-selective cleavable linker, both of which reduce off-target toxicities, and a bystander antitumor effect that can target TROP2-expressing cells in the tumor microenvironment.
In the phase I TROPION-PanTumor01 trial, Dato-DXd had promising anti-tumor activity and a manageable safety profile in patients with metastatic HR+/HER2– breast cancer, paving the way for the TROPION-Breast01 study reported here.
Efficacy results
In the Breast01 trial, 732 patients with inoperable or metastatic HR+/HER2– breast cancer previously treated with 1 or 2 lines of chemotherapy that had progressed on endocrine therapy were stratified by number of prior chemotherapy lines, geographic region, and prior CDK4/6 inhibitor status, and then randomized to either Dato-DXd 6 mg/kg intravenously on day 1 of each 3-week cycle (365 patients) or to investigator’s choice of chemotherapy (367 patients). According to the protocol, chemotherapy could be eribulin mesylate, vinorelbine, or gemcitabine delivered via IV on days 1 and 8 every 3 weeks, or oral capecitabine on days 1 through 14 of every 3-week cycle.
At the time of data cutoff, 93 patients assigned to the ADC and 39 assigned to chemotherapy were still on treatment.
As noted before, median PFS by blinded independent central review, one of two primary endpoints, was 6.9 months with Dato-DXd, compared with 4.9 months with chemotherapy, translating into a hazard ratio for progression of 0.63 (P < .0001).
The benefit was seen across nearly all subgroups except among patients who had not previously received a CDK4/6 inhibitor, and patients who had received a prior anthracycline but not a taxane.
Objective response rates (ORR) were 36.4% with Dato-DXd (99.5% partial and .5% complete response), compared with 22.9% with chemotherapy (all partial responses; P values not reported).
Overall survival data, the other primary endpoint, were not mature at a median OS follow-up of 9.7 months, and will be reported at a later date.