SAN ANTONIO — In endocrine-resistant, HR+/HER2- metastatic breast cancer, the antibody-drug conjugate (ADC) datopotamab deruxtecan (dato-DXd, Daiichi Sankyo/AstraZeneca) has greater efficacy and a better safety profile than investigator-chosen chemotherapy, according to the latest results from the TROPION-Breast01 clinical trial.
If approved, the ADC would join sacituzumab govitecan (Trodelvy, Gilead) as agents that target trophoblast cell-surface antigen-2 (Trop-2), which is universally expressed in breast cancer, according to Aditya Bardia, MD, who presented the new results at the San Antonio Breast Cancer Symposium.
“ If this drug gets approved, we need more work in terms of biomarkers of response and resistance to understand how to select these agents and how to sequence these different agents,” Dr. Bardia said in an interview. He is associate professor of medicine at Harvard Medical School and Massachusetts General Hospital Cancer Center.
Dato-DXd has a proprietary linker technology that makes it more stable in plasma and more selective for tumor cells, where overexpressed enzymes cleave it and lead to release of the drug. This reduces off-target toxicity, said Dr. Bardia.
The primary results from TROPION-Breast01, presented at ESMO 2023, showed statistically significant improvement in progression-free survival compared to investigator’s choice of chemotherapy (hazard ratio, [HR], 0.63; P < .0001) and a higher overall response rate (36.4% versus 22.9%).
At SABCS, Dr. Bardia presented additional PFS sub-analyses and safety data.
TROPION-Breast01 included 732 patients who had failed or were ineligible for endocrine therapy, and who had received 1-2 lines of chemotherapy in the metastatic or inoperable setting. They were randomized to dato-DXd or chemotherapy.
The median PFS as determined by blinded independent central review was longer in the dato-DXd group (6.9 versus 4.5 months; P < .0001). Time to first subsequent therapy was also longer (median 8.2 versus 5.0 months; HR, 0.53; 95% CI, 0.45-0.64).
PFS benefit was similar regardless of duration of previous CDK4/6 inhibitor treatment. There was no significant difference in median PFS among patients with brain metastases at baseline (HR, 0.73; 95% CI, 0.39-1.42).
Grade 3 or higher treatment-related adverse events were less common in the dato-DXd group (21% versus 45%), as were the incidences of dose interruption (12% versus 25%), treatment-related neutropenia (11% versus 42%), grade 3 or higher treatment-related neutropenia (1% versus 31%), neutropenia-related dose interruption (0% versus 17%), and neutropenia-related dose reduction (0.3% versus 13%). G-CSF usage was lower in the dato-DXd group during treatment (3% versus 22%) and after treatment (0.3% versus 8%).
Stomatitis was more common in the dato-DXd group (50% versus 13%), including grade 3 (6% versus 3%). Dose reduction due to stomatitis was also more common (12% versus 1%), and discontinuation occurred in just 1 patient (0.3%) in the dato-DXd group.
The median time to confirmed deterioration, as measured by the Global Health Status/Quality of Life scale, was longer in the dato-DXd group (9.0 versus 4.8 months; HR, 0.76; 95% CI, 0.58-0.98).
During the Q & A period after the talk, Marc E. Lippman, MD, professor of oncology and director of the breast cancer program at Georgetown University’s Lombardi Comprehensive Cancer Center, questioned the assumption that Trop-2 is universally expressed in breast cancer, and asked if there were any data on outcomes associated with its expression. “That’s a very good question,” said Dr. Bardia. He said that the team is working on the problem, including identifying the best tool to measure Trop-2 expression, but also addressing whether expression changes over time. Finally, the team hopes to determine if treatment response might relate to levels of expression.
Trop-2 expression was studied in the ASCENT trial that examined sacituzumab govitecan in metastatic triple-negative breast cancer, and there was no apparent link. “In general, we don’t see a very strong correlation between Trop-2 expression and outcomes. In the ASCENT trial, even in patients who had low expression of Trop-2, the outcomes with Trop-2 antibody drug conjugates [were] superior to standard chemotherapy,” replied Dr. Bardia.
Ron Bose, MD, PhD, also asked if there would be broader biomarker analyses of responders versus nonresponders to dato-dxd. “I think it’s very important to know, what are the biomarkers that predict efficacy for dato-dxd. The median progression free survival improvement was only about two months, maybe a little bit more, so knowing which patients are going to get the most benefit will be very important,” Dr. Bose said in an interview. Dr. Bose is associate professor of oncology at the Washington University School of Medicine in St. Louis.
Overall, he was impressed by the results. “The median progression free survival benefit is moderate, but the safety I think is really particularly strong, and when I’m thinking about this for my patients, the fact that there is a progression free survival benefit, plus a safety benefit [compared to chemotherapy] makes it very appealing,” he said.
Dr. Bose has consulted for Genentech. Dr. Bardia has been on advisory boards for Pfizer, Novartis, Genentech, Merck, Radius Health/Menarini, Immunomedics/Gilead, Sanofi, Daiichi Pharma/AstraZeneca, Phillips, Eli Lilly, Mersana, and Foundation Medicine. He has received research grants from Genentech, Novartis, Pfizer, Merck, Sanofi, Radius Health/Menarini, Immunomedics/Gilead, Daiichi Pharma/AstraZeneca, Natera, and Eli Lilly.