According to a 2016 article in the Cleveland Clinic Journal of Medicine, ischemic heart disease (a reduction in blood supply to the heart) is the most common cause of death after radiation treatments. Valve disorders and diseases of the heart muscle and the pericardial sac that encases it are also common. A disruption to the electrical pulses that make the heart pump can also occur. “Overall, compared with nonirradiated patients, patients who have undergone chest radiotherapy have a 2 percent higher absolute risk of cardiac morbidity and death at five years and a 23 percent increased absolute risk after 20 years,” the article notes.
Anju Nohria, director of the cardio-oncology program at Brigham and Women/Dana-Farber Cancer Institute in Boston, says the problem stems from radiation’s ability to kill healthy cells that are located within the field of radiation being administered to a breast cancer tumor. Radiation “essentially destroys the cancer cells preferentially because they’re rapidly multiplying and therefore more susceptible. But [radiation can] also cause some damage to any healthy tissue” nearby. She says this is particularly true for patients having radiation treatments on the left breast, as the heart sits under that breast and is therefore closer to radiation beams in some cases. “If the tumor is on the left side but in your armpit, maybe you’re fine. But if it’s right over the heart, you have a higher risk,” of developing CVD later on because of that proximity to exposure, Nohria says.
In an effort to avoid exposing the heart as much as possible, many doctors now deliver radiation treatment while patients are lying prone, “meaning that they’re lying on their stomachs with their breasts hanging down." That way, the breast is sort of separated from the chest wall, and the heart is less in the radiation field.” Radiation is delivered from the underside of the table. Some doctors are also using “very sophisticated radiation techniques where they can map out the tumor and try to exclude the heart from the radiation field to the extent possible,” she says.
Even so, some patients will experience problems while others won’t, and the risk of developing cardiac problems after radiation treatment is dependent on a number of factors, including the location of the tumor and dose of radiation administered. “If you need a lot of radiation because you have a large tumor or it’s a particularly malignant tumor,” then the higher the dose the heart may receive, Nohria says. A patient’s age and preexisting cardiac risk factors like high blood pressure, high cholesterol and diabetes can also elevate risk. Smokers or people who already have heart disease are also at higher risk, “because in a way the heart has already sustained some damage and now you’re giving it an additional kick, so to speak.”
Certain chemotherapies including anthracycline drugs and certain drugs within the Herceptin family of HER2 agonists have also been linked with an increased rate of cardiovascular disease in some breast cancer patients, Nohria says. Adriamycin, an anthracycline chemotherapy, causes a “weakening of the heart muscle in 8 to 9 percent of women. In the majority of these cases, it happens within the first year of treatment,” she says. So if you’re taking this drug, expect your doctor to keep tabs on your cardiovascular health. “As we’ve begun to realize this [risk], we’re being more vigilant looking for it in the first year after treatment.” If this cardiac toxicity is noted early, “you can put people on heart medicines that help the heart recover in a certain proportion of patients.” But a change in cardiac health won’t always be obvious early on, she says. “Sometimes you’ll have an asymptomatic decline in your cardiac function – the squeezing of the heart muscle – and it only manifests when the person comes up with symptoms, which can be a several-year lag.”
With some of the HER2 agonist drugs, cardiac problems may actually be reversible in some patients, Nohria says. “If you stop the drug, there’s a high likelihood that your heart will get better. But in a few cases, like 30 percent, it doesn’t get better. For those people, you have to manage them with cardiac medications to try to prevent it from getting worse.” Combination therapies can present additional challenges to managing cardiac disease risks. Again, as with radiation, dosage makes a difference in whether a patient will develop cardiac issues after chemotherapy. “The higher the dose, the higher the likelihood that you’ll have a problem. For instance, if you have metastatic disease and you’ve had many, many doses of the drug, your risk is higher.” Similarly, “women over the age of 60, women with preexisting risk factors and women with preexisting heart disease” all have a higher risk of developing CVD after chemo. Patients who receive a combination of chemotherapy and radiation, particularly if it’s on the left side, “have a double whammy. Plus if you’re older and have a lot of risk factors, that sort of magnifies your risk because they’re additive,” Nohria says.
As more doctors have become aware of the connection between breast cancer treatments and heart health later in life, many are taking steps to reduce the risk, particularly in patients who have other risk factors for cardiovascular disease. In many patients, this means some prep work before therapy begins. “If you’re in a good medical center, before they start you on these things they should be getting a good cardiac history and trying to optimize your cardiac risk factors before starting you on these medications,” Nohria says. Breastcancer.org also recommends that, “no matter how old you are, it’s a good idea to ask your doctor about your personal risk of treatment-related heart problems and whether or not visiting a cardiologist before treatment starts is a good idea for you.” In addition to evaluating your baseline heart function and assessing your risk factors, “you also may want to ask your oncologist how your heart function will be monitored during treatment.”
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