Women who undergo breast-conserving surgery (lumpectomy) for early-stage breast cancer usually receive radiation therapy as a part of their treatment. Radiation kills cancer cells left behind after surgery and helps prevent them from causing a recurrence or spreading to other tissues. For example, in a 2011 study in The Lancet involving more than 10,000 women treated with breast-conserving surgery, radiation cut the 10-year recurrence rate by one-third to one-half. Numerous studies have found that mastectomy (which removes the entire breast) is no more effective than lumpectomy plus radiation in improving survival rates. (Radiation may also be given after mastectomy, depending on the size of the cancer or extent of its spread.)
The main serious downside of radiation is potential damage to the heart. Several studies have found that women who receive radiation for breast cancer have an increased risk of heart disease and death from cardiac causes. It’s a special concern for women with left-sided breast cancer, because the heart is mostly in the left chest. Since the early 1990s, technical advances have been introduced to lower the risk of exposing the heart to radiation. But it’s unclear how much these newer techniques help — partly because heart disease usually develops more than 10 years after exposure, and follow-up studies have been too short. Also, it hasn’t been clear exactly how radiation damages the heart.
An important study has found that women undergoing radiation for breast cancer, especially on the left side, have an increased risk of stenosis, or narrowing, in the coronary arteries that receive the most radiation. Stenosis can block blood flow to the heart and cause a heart attack. The results, which were published online in the Journal of Clinical Oncology (Dec. 27, 2011), indicate that clinicians planning radiation must do everything possible to protect the coronary arteries.
The study. Researchers at Uppsala University in Sweden examined medical data on 8,190 Swedish women who were diagnosed with breast cancer between 1970 and 2004 and cross-checked the data with registries of coronary angiography (a treatment for blocked coronary arteries) performed in hospitals between 1990 and 2004. They found 199 women with breast cancer who went on to have coronary angiography. Before analyzing the data, the researchers identified two areas of the coronary arteries most likely to receive radiation (“hot spots”) and classified radiation regimens as having either a “low risk” or “high risk” of irradiating these areas. (High-risk regimens were more common in earlier years, when radiation was less controlled than it has been more recently.) A radiologist reviewed the angiograms and scored the degree of stenosis in several segments of the major coronary arteries.
The results. Among the 62% of women who received radiation, those with left-sided breast cancer were about four times more likely than those with right-sided breast cancer to have moderate stenosis in the coronary arteries and about seven times more likely to have severe stenosis. Women who received high-risk radiation to the left breast (or to the lymph nodes running down the left side of the sternum) were almost twice as likely to have stenosis in “hot spot” areas as those who had low-risk radiation or none.
Limitations and implications. The researchers didn’t have data on the specific radiation dose of each woman or on individual women’s risk factors for heart disease, so the magnitude of radiation’s role is unclear. Still, the results add to mounting evidence that radiation therapy for breast cancer can cause heart disease and strongly suggest that one mechanism is damage to the coronary arteries. It’s biologically plausible that radiation causes inflammation in the cells lining the arteries that eventually results in arterial stiffening and narrowing. This study is one of the first and largest to investigate the effects of radiation therapy for breast cancer on specific anatomical sites in the heart; more research is needed to find out whether other sites are affected and how. (Research from Duke University has shown that radiation can cause abnormalities in cardiac perfusion — the flow of blood through the heart muscle.)
Perspective. The findings are not a reason to choose mastectomy over lumpectomy plus radiation. A lot depends on the technologies used in radiation therapy. This study and others indicate that modern techniques help reduce the risk of heart problems. Also, not every woman who receives radiation — even radiation to the left side — will have a problem. (Only 199 women out of the more than 5,000 who received radiation required coronary angiography.) For one thing, anatomy differs from woman to woman. “The heart may be in the left chest, or it could be in the center. It may be close to the breast or not so close,” says Dr. Alphonse Taghian, chief of Breast Radiation Oncology at Massachusetts General Hospital (MGH) in Boston. Today, radiation oncologists can use CT scans and other techniques to precisely locate the heart, lung, and cancer site before choosing the angle of radiation. “In the old days, we used to treat patients all the same way. But now we have enough technologies to individualize treatment,” Dr. Taghian explains.
What to do
If you’ve recently been diagnosed with breast cancer and will be having radiation therapy, talk to your radiation oncologist about the risk to your heart, especially if you have left-sided breast cancer. Dr. Taghian suggests that you ask about the following options:
Breath-hold technique. This strategy (see the illustration) calls for the patient to take a deep breath and hold it while the radiation is given (typically about 16 seconds per radiation field). This maneuver expands the chest cavity and increases the distance between the breast tissue and the heart. In most women, it moves the heart completely out of the radiation field.
In some women, radiation given to the left breast can cross part of the heart (A). This risk can be avoided with the breath-hold technique, which moves the heart out of the radiation field ().
Partial breast irradiation (PBI). In this approach, radiation is given only to the tumor site and the area immediately around it, instead of the whole breast, and it’s given for a shorter time — a week or two, instead of six or seven weeks. PBI reduces the heart’s exposure to radiation by 85%. If you have a small, low-grade breast tumor and no lymph node involvement, you may be a candidate.
Proton therapy. Some radiation oncologists are considering the use of proton therapy for women with breast cancer who are at particularly high risk for heart damage from radiation and chemotherapy. The advantage over standard radiation (which uses photons) is that protons can be aimed and focused more precisely. Proton therapy is very expensive and hasn’t been widely used for breast cancer, but a clinical trial under way at MGH will use it for women with left-sided, advanced breast cancer.