The 65-year old woman in your clinic was diagnosed with breast cancer five years ago, when a radiologist noted a suspicious shadow on a routine mammogram. She was lucky. Her cancer was treated with lumpectomy and radiation and now – half a decade later – she is thrilled when you tell her that she remains disease-free.
In years past, she has come to your office concerned about a recurrence of her cancer. Today, more certain that she has joined the ranks of the estimated three million breast cancer survivors in the US, she presents with a different set of concerns.
For the first time, she asks you about the long-term effects of radiation therapy. A friend was recently told she had lung disease secondary to radiation therapy, she says. Furthermore, she’s read that older radiation treatments could leave patients with heart disease. Does she need to be concerned?
A new study, published in this week’s NEJM addresses your patient’s question and concludes yes, even small amounts of radiation for breast cancer are tied to increased risk of cardiovascular disease.
Sarah Darby and colleagues examined hospital records of women in Sweden and Denmark who had received radiation for breast cancer from 1958 to 2001 and suffered a major coronary event after their diagnosis and treatment. They compared these records to controls – women with breast cancer diagnoses, who had received radiation therapy, but who did not have a history of heart attack, coronary revascularization or death from ischemic heart disease.
In all, the authors collected nearly 1000 cases and 1200 controls. Through chart review and virtual simulation, the authors determined the mean radiation dose to the heart and, specifically, to the left main coronary artery for each woman.
Comparing cases to controls, they found that the risk of ischemic heart disease increases in a linear fashion by 7.4 percent with each incremental Gy (the unit of measurement) of radiation exposure to the heart. There was no threshold minimum level of radiation below which there was no damage. The increased risk started five years after radiation, and persisted for at least two decades. In women with preexisting heart disease, the risk only increased.
These results are not perfect. First, the authors acknowledge, they included few women younger than 40 at the time of breast cancer diagnosis. And no one in the study received certain chemotherapeutics, such as taxanes, which are themselves known to cause cardiac damage. Despite these limitations, the conclusions are provocative.
What to do?
In an accompanying editorial, cardiologist Javid Moslehi argues that this study should spark “greater collaboration” between cardiologists and oncologists. He describes a burgeoning field of “Cardio-Oncology,” which deals with the cardiovascular complications of cancer treatments. He notes that this interdisciplinary team should be involved early – before complications develop.
“An important lesson for the oncologist may be that cardiovascular “survivorship” concerns should begin at the time of cancer diagnosis… not as an afterthought” Moslehi writes. “Similarly, cardiologists need to consider prior radiation therapy exposure as the significant cardiovascular risk factor it is.”