Study details
The investigators enrolled 58 patients – 56 pre- and postmenopausal women and 2 men – with HR+/HER2-low tumors determined by local and/or central review, and operable stage II or III cancers.
After stratification by HER2 expression level and menopausal status, the patients were randomized to receive either T-DXd alone at a dose of 5.4 mg/kg, or with T-DXd at the same dose plus anastrozole, with men and premenopausal women also receiving a gonadotropin-releasing hormone analog.
The protocol originally called for six cycles of therapy, but was amended in February 2022 to increase the number to eight for newly enrolled participants and patients who were already on study treatment but had not yet had surgery.
The majority of patients in each arm had invasive ductal cancers, and most had HER2 expression on immunohistochemistry (IHC) of 1+, which is generally considered to be HER2-negative. However, there was only modest concordance between local and central review in determining HER2 expression levels, Dr. Bardia noted. Indeed, the entire question of HER2-low cancers, whether they compose a separate clinical entity from other cancers and how to standardize testing, was the subject of a special session at this year’s SABCS.
Results
Overall response rate, the primary endpoint, was 68% in the T-DXd arm and 58% in the T-DXd plus anastrazole arm.
Although the low response rate with the combination suggests that endocrine therapy may not be helpful in this patient population, it’s still too early to say so conclusively, Dr. Bardia said.
Looking at the change in HER2 expression by IHC from baseline to surgery, they found that 48.6% of patients had a change in HER2 IHC expression after T-DXd treatment, and that nearly 90% of these patients had a decrease in expression levels.
Among 42 patients with available data on residual cancer burden (RCB) at the time of data cutoff, one patient in the T-DXd alone arm with stage 3A disease had an RCB of 0, equivalent to a pathologic complete response (pCR). There were no other RCB 0 tumors after surgery in either study arm. The rate of combined RCB and RCB 1 (near pCR) was about 15% in each arm.
In all, 3 of the 58 patients in the study (5.2%) required dose reductions because of adverse events. There were no cases of grade 3 or greater pneumonitis, and no cases of either cardiomyopathy or neuropathy.
Way better than chemotherapy?
“It was very exciting when we got the DESTINY-Breast04 results showing this impressive activity of trastuzumab deruxtecan in this HER2-low entity, and now we know that hormone-positive [tumors], the majority of them are HER2-low. It was really encouraging, it was practice changing, but we were left wondering about this HER2-low entity, and can we act on it in the earlier setting,” commented Jason A. Mouabbi, MD, from the University of Texas MD Anderson Cancer Center in Houston.
“The beauty of the TRIO-US B-12 TALENT study is that it looked at the neoadjuvant setting where we know those patients who are hormone-positive usually do not respond well to chemotherapy,” he said in an interview.
He said that although the study didn’t compare T-DXd to chemotherapy, “it’s an excellent first start.”
An overall response rate near 70% “is something amazing. I’m really excited to see it against chemo. I think it’s going to do way better,” Dr. Mouabbi said.
The study was conducted by the Translational Research In Oncology (TRIO)-US network. Funding was provided by Daiichi Sankyo, the maker of trastuzumab deruxtecan (Enhertu). Dr. Bardia serves as a consultant or advisory board member for Pfizer, Novartis, Genentech, Merck, Radius Health, Immunomedics/Gilead Sciences, Sanofi, Daiichi Sankyo, AstraZeneca, and Eli Lilly, and has received research funding from Genentech, Novartis, Pfizer, Merck, Sanofi, Radius Health, Immunomedics/Gilead Sciences, Daiichi Sankyo, AstraZeneca, and Eli Lilly.
Dr. Mouabbi disclosed honoraria from BostonGene, Cardinal Health, Napo Pharmaceuticals, and Fresenius Kabi.