Doctors and patients are paying closer attention to ADC heart risk as these targeted cancer drugs reach more people with breast cancer. Antibody drug conjugates have changed how oncologists treat several subtypes of the disease. But understanding what they do to the heart matters just as much as understanding what they do to the tumour. This conversation is now urgent across the medical community.

What Are Antibody Drug Conjugates?

Antibody drug conjugates (ADCs) are a targeted class of cancer medicines. They attach a chemotherapy payload to an antibody that seeks out cancer cells, delivering the toxic drug directly to the tumour. In theory, healthy tissue elsewhere stays protected. That precision has made ADCs a genuine step forward in oncology.

Trastuzumab deruxtecan (T-DXd) is one of the most widely used agents today. The FDA approved it for HER2-low metastatic breast cancer after the DESTINY-Breast04 trial. That 2022 New England Journal of Medicine study showed T-DXd pushed progression-free survival from 5.4 months to 10.1 months compared to standard chemotherapy. A meaningful result. But wider use brings a wider lens, and the heart needs to be part of that picture.

ADC Heart Risk: Why It Matters

ADC heart risk varies between agents, and clinicians should not dismiss it. A 2025 meta-analysis in JAMA Network Open looked at cardiac outcomes across 12 T-DXd trials covering 4,847 patients. About 4.2% experienced a meaningful drop in left ventricular ejection fraction (LVEF), the standard measure of how effectively the heart pumps blood. The older ADC trastuzumab emtansine (T-DM1) showed that same drop in under 1.1% of patients. That is roughly a 3.8-fold difference.

Real-world data make the picture more serious. The FDA Adverse Event Reporting System shows cardiac events tied to T-DXd carry a case fatality rate of around 22%. Older HER2-targeted therapies sit at 8 to 12%. Clinicians believe late detection drives part of this gap. Many patients also arrive at ADC treatment after rounds of anthracycline-based chemotherapy, which quietly damages the heart muscle over time, even before scans pick it up.

Why Some Patients Face Greater Risk

Not all patients carry the same level of ADC cardiotoxicity risk. Key vulnerability factors include prior anthracycline exposure, a baseline LVEF between 50 and 54%, age over 65, conditions like diabetes or hypertension, and earlier use of HER2-targeted agents such as trastuzumab or pertuzumab.

Researchers call one mechanism the “anthracycline sensitisation” effect. Prior chemotherapy can leave the heart more reactive to the stress that newer ADCs introduce. The DESTINY-Breast11 neoadjuvant trial supports this. Patients there, who carried less prior anthracycline exposure, showed a cardiac event rate of just 1.3%. That compares to 4.2% in more heavily pretreated groups. The prior treatment history clearly shapes how much ADC heart risk a patient carries.

How ADC Cardiotoxicity in Breast Cancer Differs From Older Therapies

ADC cardiotoxicity in breast cancer works differently from the toxicity clinicians saw with older HER2-targeted drugs. Trastuzumab blocks a signalling pathway the heart uses for repair. That tends to reverse once treatment stops and cardiac medications begin.

T-DXd may cause a different kind of injury. Its cleavable linker system releases the toxic payload, called DXd, into surrounding tissue, not just inside the cancer cell. DXd crosses cell membranes easily. Researchers think this bystander effect might let free drug reach heart tissue. That said, this remains a hypothesis. Laboratory studies still need to confirm it.

TROP2-directed ADCs tell a different story. Sacituzumab govitecan and datopotamab deruxtecan, which oncologists use mainly in triple-negative breast cancer, show minimal cardiac signals in trials. The ASCENT trial recorded cardiac events in under 1% of patients. TROPION-Breast01 came in at 0.8%, in line with background rates. The ADC heart risk pattern appears specific to T-DXd rather than shared across the whole drug class.

Monitoring and Protecting Heart Health

Expert consensus now supports a risk-stratified monitoring approach for patients on next-generation ADCs.

Standard-risk patients on T-DXd (no prior anthracycline use, preserved heart function, no major comorbidities) need echocardiography every nine weeks plus baseline biomarker testing. High-risk patients need more. Clinicians recommend echocardiography every six weeks, monthly high-sensitivity troponin and NT-proBNP checks, and a cardiac specialist involved throughout treatment.

Global longitudinal strain (GLS) offers a more sensitive read than standard LVEF measurement. Experts increasingly recommend it at baseline and during treatment. Studies show that troponin rises during the first two cycles of T-DXd can predict later heart function decline. That early signal creates room to act before symptoms appear.

Patients moving from T-DXd to a TROP2-directed ADC should get a washout echo six weeks after their last T-DXd dose. That echocardiogram, including GLS, catches any subclinical changes before the next treatment starts.

Looking Ahead

AI-assisted echocardiography is one area gaining traction in cardio-oncology. Automated platforms measure ejection fraction with less variability than conventional methods. That consistency matters most in the narrow LVEF range where clinicians decide whether to continue, pause, or stop treatment.

The field still needs dedicated cardiac sub-studies inside ADC registration trials. Long-term survivorship data from early-stage programmes remain thin. Randomised trials on early cardioprotective medications are also underway. Results from phase II studies on these strategies are expected in 2026 and 2027.

Better cancer outcomes should not come at the cost of heart health. Clinicians and patients who stay on top of ADC heart risk give themselves the best chance at outcomes that hold up on both fronts.

Source: cureus