SAN Antonio – How do you shoot at an invisible target? It seems counterintuitive, but
Dr. Aditya Bardia
In the investigator-initiated TRIO-US B-12 TALENT study looking at neoadjuvant T-DXd either alone or in combination with the hormone therapy anastrazole, the objective response rate (ORR) with T-DXd alone was 68%, compared with 58% for T-DXd plus anastrazole, reported Aditya Bardia, MD, MPH, a medical oncologist with Massachusetts General Hospital Cancer Center in Boston. He recently presented the study findings at the 2022 San Antonio Breast Cancer Symposium.
“The study provides a rich platform for additional translational research to evaluate more sensitive methods of HER2 detection, develop predictive biomarkers, and understand mechanisms of resistance in residual disease which would guide subsequent therapeutic strategies, including combination therapy,” he said in an oral abstract session at the meeting.
Not-so-innocent bystander
In an interview, Dr. Bardia explained that the T-DXd may have efficacy in HER2-low cancers because of a bystander effect.
“With these antibody drug conjugates, if you have the antigen, the ADC binds to the antigen, gets internalized, and releases the payload, but the payload has a bystander effect ... it’s membrane permeable, so it can go outside and affect other cells that do not express the antigen. So for HER2-low tumors, even if there is HER2 heterogeneity or if there are some cells that do not express HER2, this would work because of the bystander effect,” he said.
Although neoadjuvant chemotherapy with an anthracycline and taxane is often used to treat patients with high-risk localized HR-positive breast cancer, the therapy is associated with low pathologic complete response (pCR) rates, radiological response rates of around 50%, and significant toxicities, including myelosuppression, neuropathy, cardiomyopathy, and leukemia risk, Dr. Bardia said.
At cross purposes
The trial included both a T-DXd monotherapy arm and a second arm containing the antibody drug conjugate (ADC) with endocrine therapy. The rationale for the latter is that there is documented “cross-talk” between the estrogen receptor (ER) and HER2.
“In tumors that become endocrine resistant, you see an increase in the HER2 pathway, and if you block ER, you see that HER2 goes up and vice versa. If you just block HER2 alone, the expression of ER can go up, and if you block the PI3 kinase alone, the expression of ER goes up,” he said.
Dual blockade can be effective with antibody-based therapy or with tyrosine kinase inhibitors, but with an ADC, the dual blockade strategy may be less effective, Dr. Bardia said, “because if you have an ADC, you need HER2, the ADC binds to HER2, then gives the payload to the cancer cells and essentially kills the cancer cells,” Dr. Bardia explained in a media briefing held prior to his presentation.
In fact, the T-DXd–anastrozole combination was associated with a lower overall response rate in the study than T-DXd alone, but Dr. Bardia cautioned about overinterpreting these results, as the study included only 39 patients.