CHICAGO — Indications are expanding, new agents are emerging, combinations with other drug classes are being tested, and many patients with this disease are now receiving more than one ADC.
ADCs use antibodies to bind to the surface proteins of cancer cells to deliver a potent payload of cytotoxic chemotherapy. Three are approved for use in pretreated patients with metastatic breast cancer: sacituzumab govitecan, or SG, for patients with triple-negative disease; trastuzumab deruxtecan, or T-DXd, for patients with HER2-positive and HER2-low disease; and trastuzumab emtansine, or T-DM1, for patients with HER2-positive disease. A fourth agent, datopotamab deruxtecan, or Dato-DXd, is being assessed by the US Food and Drug Administration (FDA) for use in pretreated HR-positive, HER2-negative patients, and others, including sacituzumab tirumotecan, are being tested in clinical trials.At the annual meeting of the American Society of Clinical Oncology, T-DXd (Enhertu, AstraZeneca) showed better progression free survival than chemotherapy in people with HR-positive, HER 2-low metastatic breast cancers. These findings, from the DESTINY Breast-06 trial, were among the most talked-about at ASCO, and are likely to change clinical practice (J Clin Oncol. 2024;42[suppl 17; abstr LBA1000]).
But other ADC results presented at ASCO showed that there is still much to be worked out about the timing and sequencing of these agents, as well as their synergy with other drug classes, in metastatic breast cancer.
An ADC gets its first test, and falls short
Antonio Giordano, MD, PhD, of the Dana-Farber Cancer Institute in Boston, presented findings from an open-label phase 2 study of the ADC enfortumab vedotin (EV), an agent currently approved for use in advanced or metastatic urothelial cancer, at ASCO. This study included two cohorts of previously treated metastatic breast cancer patients: one with triple-negative disease (n = 42) and the other with HR-positive HER2-negative (n = 45).
Dr. Giordano and his colleagues’ study is the first to look at this ADC in breast cancer. EV’s antibody targets the cell adhesion molecule Nectin-4.
The researchers found that though EV demonstrated anti-tumor activity in both cohorts — with 19% of the triple-negative patients and 15.6% of the HR-positive/HER2-negative patients responding — the results did not meet the prespecified response thresholds for either cohort. (J Clin Oncol. 2024;42[suppl 16; abstr 1005]).
In an interview, Dr. Giordano said that studies in urothelial cancer had shown better response to EV associated with more expression of Nectin-4, but this study did not see such clear associations between expression and response. While there is no question that Nectin-4 is highly expressed in breast cancer and therefore a viable target, he said, “it may need to be looked at a little more deeply.”
It could also be the case, Dr. Giordano said, that the effect of EV’s payload may have been less robust in participants who had been previously treated with taxane chemotherapy, as nearly all patients in the two cohorts were.
“Taxanes are microtubule disruptors. And with this drug we had a payload with pretty much the same mechanism of action,” Dr. Giordano said. Ideally, he said, he would like to test the agent in a first-line setting, possibly in combination with an immunotherapy agent.
The timing of ADCs is as important as their targets and their payloads — and something that investigators are still struggling to figure out, he said.
A third of the patients in the triple-negative cohort of his study had been previously treated with SG, and a handful of individuals with T-Dxd, he noted.
“We’re in the middle of an ADC revolution,” he said. “It’s really key to figure out the best sequencing for a patient and if it’s actually worth it to do it. Very often we see patients respond best to the first ADC. But sometimes we see patients that do not respond to the first ADC and then they respond to the second one. It’s not very frequent, but it happens.”