A recent study found mammograms may be better at identifying breast cancer in some women during the first week of their menstrual cycle. We spoke with Dr. Diana Miglioretti, a senior investigator at Group Health Research Institute in Seattle, one of the study’s researchers, about the accuracy of mammograms and the impact of mammograms and other imaging tests on cancer risk.
Q: Your study showed that the timing of a woman's mammogram within her menstrual cycle may affect the accuracy of her mammogram results. Are there any other factors that may affect mammograms that we are just beginning to understand?
A: Yes. I'd say that the interpretation of mammography…varies wildly across radiologists and across facilities.
It's important that when you make your appointment for a mammogram , to ask if there's a breast-imaging specialist available to read the mammogram. That's what I would do. I'd rather drive a farther distance to have a breast-imaging specialist read my mammogram than go to a close facility that doesn't have one available.
We found that breast-imaging specialists are more accurate at interpreting mammograms. [Also] radiologists who are fellowship-trained in breast imaging are better at interpreting mammograms.
There are also some patient-level factors that influence mammography performance: patients' age in addition to breast density; whether you have a family history of breast cancer — one with a family history of breast cancer might expect more false positive mammograms, meaning they're going to be more likely to be recalled for benign breast disease than other women.
Also, your time between your screening mammograms — if you have more time in between screening mammograms, the tumor has more time to grow and it's easier to detect larger tumors.
Q: So a woman's age can influence the accuracy of her mammogram results. Is this because breast density is lower in menopausal women?
A: Age is associated with accuracy above and beyond breast density, so it's not just breast density, but there's something else about older women that makes it easier for a mammogram to see cancer and to rule out cancer.
Q: You are also studying the possible impact of more frequent diagnostic imaging. Is there evidence that more medical imaging tests may raise someone's risk of cancer?
A: Yes. This gets more to CT — computed tomography. The use of CT in the United States has grown rapidly in the past two decades. The dose from CT is in the range where it can increase the risk of cancer. So I do believe that our increased use of imaging could be causing cancer.
Q: Can frequent mammograms increase the risk of breast cancer?
A: The radiation from mammograms is pretty low. So the use of mammograms could increase cancer slightly, but the benefits of mammograms in women 50 and over outweigh the risk.
This is not true for women under 40. Unless you have very strong risk factors for breast cancer, such as a strong family history, such as BRCA1 or 2 mutations, it's not recommended that women under 40 get mammograms, because the risk of cancer from that mammogram could outweigh any benefit.
Q: Would that be because the women who start the mammograms earlier receive them over a longer period of time?
A: That's correct. And younger women may be more susceptible to radiation-induced cancer. So, the effect of radiation on inducing cancer depends strongly on age, with children being at the highest risk. So young adults can be at a pretty high risk of radiation-induced cancer.
Once you're in your middle ages, there may not be any more decline, but they're at lower risk.
Q: Back to the CT scans. What would you say about weighing the risks and benefits of that type of imaging?
A: That's unknown. That's an area that needs to be researched.
If a person has some acute condition that could lead to their imminent death, then it's very important to have the imaging. So it's very dependent on the indication for the exam.
And that's research we're proposing to do, is to look at some indications for CT imaging and see when it really does have a benefit that outweighs the risk.
But if possible, there's ways to reduce the risk of cancer .
One, you need to just make sure whether you really need the imaging test — has a prior imaging test been done? Are there other imaging tests you can use that don’t have radiation, like MRI or ultrasound?
And then if the doctor determines that the CT really is needed, there are low dose protocols or ways to reduce the dose from CT that should be considered, especially in young children.
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