What's the Connection? Breast Cancer and Heart Disease
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I started my journey in public health as an intern for Susan G. Komen for the Cure in Washington D.C. During a 5k walk event on the National Mall; we lobbied for signatures ensuring that women would receive mammograms by age 40. Many signed without even reading our sheet. I remember one woman, she practically ripped the clipboard from my hands saying something along the lines of, "I'll sign. Women needed to e screened and get treated immediately."
That is the conventional line of thought. When individuals are diagnosed with breast cancer they tend to undergo radiation therapy or sometimes a mastectomy. Komen, the CDC, and the American Cancer Society support these treatment measures. But a recent article from the New England Journal of Medicine, demonstrates that this treatment can cause a small increase in the risk of heart disease in women who undergo radiation of the breast.
The study
A team of researchers from the University of Oxford conducted a study from over 40 years of data ranging from 1958 to 2001. Using medical records, the researchers took an in-depth look at 2168 women from Denmark and Sweden who had breast cancer radiation treatment. Within this group, 963 died as a result of cardiac related illness and 1205 served as controls.
Including:
- Heart attacks
- Blocked or replaced blood vessels
- Death (ischemic heart disease)
Findings
The authors found that exposure to radiation for breast cancer causes a small increase in risk for major coronary events. The greater amount of radiation a patient has, also contributes to a small increase in risk. In addition, having known risk factors for heart disease contribute to this problem.
Conditions such as:
- Circulatory diseases
- Diabetes
- Chronic obstructive pulmonary disease
- Overweight
- Smoker
The average amount of radiation a woman experiences is 4.9 grays. A gray or Gy is the unit of measure for the absorbed dose of radiation into the body. The study had patients with Gys ranging from .03 to 27.2 grays.
The researchers quantify this increased risk by using hypothetical examples to demonstrate the small amount of risk associated with treatment.
| Female Patient –age 50Treatment: 3-gray dose radiation | Risk of death from ischemic heart disease before 80 years old | Increase in risk (%) |
| No known heart-related risk factors | 1.9% to 2.4% | 0.5% |
| History of a single heart-related risk factor | 3.4% to 4.1% | 1.7%. |
What does this mean for breast cancer treatment?
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We known that radiation treatment for breast cancer works, but this study demonstrates other negative health effects that can potentially result from a standard treatment. The important thing is that this information needs to be shared. Doctors have a responsibility to be aware of this finding and report it to their patients if they are undergoing radiation.
Awareness of this increased risk should be taken into consideration by patients as they consider treatment options. This holds even greater importance for individuals who have known risk factors. To decrease the risks of heart disease later in life the researchers recommended that after treatment, patients take steps to reduce their risk of heart disease. Such as maintaining a healthy diet and weight, exercising and being a nonsmoker.
Communicating Risk
Understanding the risks that this treatment can cause are very difficult to understand. I even had to look at the numbers multiple times to make sure I fully understood what they meant and their implications. I didn't really like the authors use of a female patient who's 50 years old with no known risk factors versus the same 50 year old woman with a heart disease risk factor. I'm no expert but I don't think all breast cancer patients fit into these two categories. It's much more complex than that.
One thing that did help me understand was the linear relationship. The more gray's your body receives during treatment increases your risk of heart disease. But what does that fraction of a percent increase mean? This is one of the hardest questions in health regarding numeracy. The ability to interpret quantitative numbers in regards to health information. Take the increase for a woman with no history of heart disease risk factors. For women like her, a 0.5% increase in death means 1 additional woman out of 200 will die from heart disease or related problems by age 80. For similar women with a risk factor an additional 2 out of 200 women will die from heart disease or related problems by age 80. The amount of additional women out of 200 increases as the amount of gray's increases.
When dealing with small increases in risk, what the number means can sometimes be difficult to understand. It is important to remember that the increased risk in heart disease is small. However, the increased risk, no matter how small, need to be communicated to the patient so they can make an informed decision about their health. I am by no means an expert in numeracy, so the next challenge is for someone better to come along with an even better way of communicating the increased risk in a concrete and simple way. Any takers?
Source: Risk of Ischemic Heart Disease in Women after Radiotherapy for Breast Cancer. Published in the March 14, 2013 issue of the New England Journal of Medicine (Vol. 368, No. 11). First author: Sarah C. Darby, PhD, University of Oxford, Oxford UK.
-- Nandakumar
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