Ask-the-Expert Online Conference
- Question from KVY: Could the X-rays women are exposed to and the compression during mammograms be an environmental element that could contribute to women getting breast cancer?
- Answers - Devra Davis It depends on the age of the person getting the mammogram and the amount of exposure involved. Unfortunately, younger women are at a higher risk from radiation than are older women. We know this because of the data developed from Hiroshima where young girls and women under the age of 20 who were exposed to radiation had a much higher risk of breast cancer when they reached middle age. But women who were already middle-aged when exposed to the radiation at Hiroshima did not show this increased risk. So diagnostic radiation from mammography in women under 40 or possibly in women before menopause in general may well carry an increased risk of cancer associated with radiation alone. We certainly know that radiation of a pregnant woman will increase the risk of leukemia in her offspring.
- Jennifer Griggs, M.D., M.P.H. We generally consider radiation therapy much more dangerous in a pregnant women than chemotherapy, which surprises many people.
- Sue Heffelfinger There are studies of children who have been irradiated for specific diseases such as Hodgkin's, who developed breast cancer later on. So there really is a childhood age range where radiation should be kept to an absolute minimum.
- Jennifer Griggs, M.D., M.P.H. At the University of Rochester, we have done much of that work, looking at age of therapeutic radiation and breast cancer risk and have demonstrated that therapeutic radiation around the ages of 10 to 14 has the highest risk, and that's when breast tissue is considered to be proliferating [growing].
I have a sad personal comment—when my daughter was 10, we rushed to the hospital because she might have had a ruptured spleen. This is a serious issue, so they wanted to do a CAT scan. And CAT scans, as we know, contain higher doses of radiation.
I asked the young radiologist who was a woman if she would shield my daughter's nipple area, and she looked puzzled and asked why. I explained her breasts would be developing. She said, “She doesn't have any!” I told her the vulnerability to the cancer-causing effects of radiation is dependent on the rapid cell growth of a young girl, and this young radiologist was really perplexed. So I took my gloves and held them over my daughter's chest area because I was concerned. As others have just said, we know very well that the younger the age at first exposure (and particularly when exposure takes place at a time of great development), the greater the risk.
- Sue Heffelfinger That is a very sensitive period, but mammary glands undergo periods of growth with each menstrual cycle. Radiation sensitivity probably lasts well beyond that early stage.
- Devra Davis That's very interesting. Has anyone ever looked at whether or not the timing of mammography could have an effect, in terms of a woman's cycle?
- Sue Heffelfinger Certainly the risk hasn't been found to be that definitive, so I don't know of any data off the top of my head. Cycle time and time of surgery has been studied, but I don't think there's been any study of risk of mammography and cycle time.
- Devra Davis It might make a lot of sense. There's a lot we don't know. But we have some good scientific reasons to be concerned about some things. And I think what we're saying right now is that the timing of exposure can be as important as the dose. So that exposure to the very young girl is important, but even exposure at the time of greater cell growth of the breast in a more mature woman who is still having a menstrual cycle could still be important. So you might want to not have mammography towards the end of a menstrual cycle because that's the time the breast is in a proliferative state [when more cells are growing].
- Jennifer Griggs, M.D., M.P.H. I think we should clarify we're not talking about one, and only one, mammogram. We're talking about cumulative doses of radiation, that is, the build-up of many doses of radiation over time.
- Devra Davis Of course, it's the cumulative dose.
- Jennifer Griggs, M.D., M.P.H. I'm wondering if the lack of compelling data supporting the use of mammography in women under 50 is because for every good that we do, we also may be undoing that with some exposure.
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