Clinical Implications of DESTINY-Breast06
The DESTINY-Breast06 data show that “we have to again change how we think about HER2 expression. Even very low levels of HER2 expression matter, and they can be leveraged to improve the treatment for our patients,” said Ian Krop, MD, PhD, of the Yale Cancer Center in New Haven, Connecticut, during the session where the results were presented.
But T-DXd may not be an appropriate first choice for all patients, especially given the safety concerns associated with T-DXd, he continued. With overall survival and quality-of-life data still lacking, clinicians will have to determine on a case-by-case basis who should get T-DXd in the first line.
“For patients who have symptomatic metastatic disease, who need a response to address those symptoms, those in whom you think chemotherapy may not work as well because they had, for example, a short recurrence interval after their adjuvant chemotherapy — using T-DXd in that first-line setting makes perfect sense to take advantage of the substantially higher response rate compared to chemo,” Dr. Krop said. “But for patients who have asymptomatic low burdens of disease, it seems very reasonable to consider using a well-tolerated chemotherapy like capecitabine in the first line, and then using T-DXd in the second line.”
In an interview, Erica Mayer, MD, of the Dana Farber Cancer Institute in Boston, Massachusetts, said patient choice will also matter in determining whether T-DXd is a first-line option. The known toxicity of T-DXd was underscored by the latest findings, she noted, while capecitabine, one of the chemotherapy choices in the control arm of the study, “really reflects what the majority of breast cancer doctors tend to offer, both because of the efficacy of the drug, but also because it’s oral, it’s well tolerated, and you don’t lose your hair.”
DESTINY-Breast07 Results
The DESTINY-Breast07 findings, from a Phase 1B open-label trial measuring safety and tolerability, were presented by Fabrice Andre, MD, PhD, of Université Paris Saclay in Paris, France. Dr. Andre and his colleagues presented the first data comparing T-DXd monotherapy and T-DXd with pertuzumab — a monoclonal antibody targeting HER2 — as a first-line treatment in patients with HER2-overexpressing (immunohistochemistry 3 and above) metastatic breast cancer. (J Clin Oncol 42, 2024 [suppl 16; abstr 1009]).
Current first-line standard of care for these patients is pertuzumab, trastuzumab, and docetaxel, based on results from the 2015 CLEOPATRA trial. T-DXd is currently approved as a second-line treatment.
Dr. Andre and his colleagues randomized 75 patients to monotherapy with T-DXd and 50 to combined therapy, with a median follow-up of 2 years.
After 1 year of treatment, combination of T-DXd and pertuzumab was seen to be associated with a progression-free survival of 89% at 1 year (80% CI, 81.9-93.9), compared with 80% in patients treated with T-DXd alone (80% CI, 73.7-86.1). Objective tumor response rate was 84% for the combined therapy at 12 weeks, with 20% of patients seeing a complete response, compared with 76% and 8%, respectively, for monotherapy.
As in the DESTINY-Breast06 trial, adverse events were high, with interstitial lung disease seen in 9% of patients in the monotherapy group and in 14% of the combined-therapy patients, although no treatment-related deaths occurred.
A randomized phase 3 trial, DESTINY Breast09, will now compare the monotherapy and the combined therapy with standard care.
T-DXd has seen a rapidly expanding role in treating breast and other solid tumors. The DESTINY Breast06 findings will move up its place in the treatment algorithm for metastatic breast cancer, “allowing us to now offer T-DXd as the first chemotherapy choice for patients who are making that transition to chemotherapy over many of the traditional provider choices that we previously have offered,” Dr. Mayer said.
The results “support the use of not only this specific agent, but also the concept of antibody drug conjugates as a very effective way to treat malignancy,” she added.
Dr. Curigliano reported receiving speaker’s fees, research funding, and other support from AstraZeneca and Daiichi Sankyo, among other companies, as did most of his co-authors, of whom three were AstraZeneca employees. Dr. Fabrice disclosed receiving research funding, travel compensation, and/or advisory fees from AstraZeneca and other entities, as did several of his co-authors. Two of his co-authors were employed by AstraZeneca and Roche, manufacturers of the study drugs. Dr. Krop and Dr. Mayer disclosed relationships with AstraZeneca and others.