Modern breast cancer screening and treatment have transformed survival. Many women now live long and healthy lives after diagnosis, thanks to increasingly effective chemotherapy and targeted therapies: medicines designed to attack particular features of cancer cells.
But as cancer outcomes improve, another challenge has become more apparent: protecting the heart from the side-effects of treatment.
Some breast cancer treatments can affect heart health. These include anthracyclines, a group of chemotherapy drugs, and trastuzumab, a targeted therapy used to treat HER2-positive breast cancers: cancers that have high levels of HER2, a protein that helps cells grow and divide.
In some patients, these treatments can weaken the heart’s ability to pump blood around the body or contribute to heart failure. Other cancer treatments can increase the risk of abnormal heart rhythms.
Early changes may not cause obvious symptoms. By the time a patient experiences breathlessness, fatigue or palpitations, the sensation that the heart is pounding or beating irregularly, damage may already have occurred.
A small study, which is yet to be peer reviewed, suggests that regular blood tests and heart traces could help doctors detect warning signs earlier.
Researchers followed 50 women with stage 1 to 3 breast cancer, cancer that had not spread to distant organs, through six cycles of chemotherapy. They measured cardiac troponin I, a protein released into the blood when heart muscle cells are injured. They also recorded electrocardiograms (ECGs), which measure the electrical activity controlling the heartbeat.
They found that troponin levels rose during treatment. ECG abnormalities also became more common, including prolonged QT intervals, which is the time the heart’s lower chambers take to contract and prepare for the next beat. If this takes longer than usual, the risk of a dangerous irregular heartbeat can increase.
Larger studies are needed to confirm these findings, but the research adds to evidence that signs of heart stress can sometimes be detected before a patient develops symptoms.
Troponin and heart health
Troponin tests have been used for more than two decades to help diagnose a heart attack (myocardial infarction).
A raised troponin level does not always mean that someone has had a heart attack, because heart damage can have other causes. During chemotherapy, raised levels may reveal small amounts of heart muscle damage before conventional measures of heart function begin to worsen.
A 2004 report identified troponins as promising biomarkers: measurable signs in the body that can indicate injury or disease.
A later clinical study found that persistently raised troponin levels during high-dose chemotherapy predicted a decline in the pumping ability of the left ventricle, the heart’s main pumping chamber. Troponin may therefore offer an early warning that a patient is at greater risk of future heart problems.
Adding pieces to the puzzle
Established forms of heart monitoring remain important. One commonly used measure is left ventricular ejection fraction, or LVEF. This is the percentage of blood pumped out of the left ventricle with each beat. It is usually assessed using an echocardiogram, an ultrasound scan of the heart.
Echocardiograms remain central to heart monitoring during cancer treatment. But LVEF can remain normal while subtler changes are developing.
Doctors can also use a measure called global longitudinal strain, which looks more closely at how well the heart muscle squeezes and relaxes. It may reveal changes before they show up in the ejection fraction.
Blood tests and ECGs could provide additional pieces of the puzzle. An ECG is quick, painless and widely available. Some chemotherapy drugs can disrupt electrical activity in heart cells, increasing the risk of abnormal rhythms, or arrhythmias. Regular ECG monitoring may help to identify patients who need closer observation.
A more personalised approach
A raised troponin level does not necessarily mean that a patient will develop heart failure. An abnormal ECG does not guarantee a serious irregular heartbeat. These tests identify signs that the heart may be under strain and help doctors assess risk.
The emerging field of cardio-oncology focuses on protecting the heart health of people with cancer before, during and after treatment.
Doctors are increasingly tailoring monitoring to each patient’s risk. Existing heart health, age, blood pressure, diabetes risk and previous exposure to treatments that may damage the heart can influence the level of monitoring required.
If doctors detect rising troponin levels or ECG changes, they may carry out tests more frequently, refer the patient to a heart specialist with expertise in cancer care or consider treatments intended to protect the heart.
This does not necessarily mean stopping cancer treatment. The aim is to manage risks while allowing patients to continue receiving effective care wherever possible.
The latest research does not provide a standalone test for predicting who will develop heart problems after breast cancer treatment. Troponin levels and ECG changes must be interpreted alongside other information. Scientists still need better evidence about how early warning signs should influence treatment decisions.
But the principle is important. As more people survive breast cancer, protecting their long-term health becomes increasingly urgent. The goal is no longer simply surviving cancer. It is maintaining heart health after treatment has ended.
David C. Gaze does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.