A Conversation About Alternative Approaches to Breast Cancer Screening
There is currently no official role for CT in breast imaging. Should there be?
Mary Salvatore, MD, MBA, had been working as a breast radiologist at Montefiore Hospital in the Bronx for five years when her boss presented her with an exciting opportunity. She could go with him to Staten Island University where they would develop a radiology residency from scratch, a dream job for Salvatore. There was only one condition, he told her: she would have to become a chest radiologist, because that was the need at Staten Island.
"I respected him very much and would have done anything he asked me to do," Salvatore remembers. She got to work studying the chest, which meant spending the majority of her day reading X-rays and computed tomography (CT) scans, instead of mammograms and ultrasounds. Salvatore loved the chest. "But I did see that on chest scans, I was seeing the breasts," she says. "And I couldn't help but know what I knew from five years of experience of looking at the breasts."
Now a chest radiologist at Columbia University Irving Medical Center and NewYork-Presbyterian, Salvatore's unusual path to her specialty has led her to ask questions which she is beginning to answer through her research, namely, is there a role for CT in breast cancer screening?
Salvatore believes there is. She has teamed up with Elise Desperito, MD, chief of breast imaging, in what Salvatore describes as an unusual partnership. "If you've been doing mammography your whole life, I can imagine you're not going to believe that anything else could be better than mammography," she says. "To have somebody from breast imaging who will look at this with me is wonderful."
In a retrospective study, Salvatore and Desperito looked at scans from 708 women who had both mammograms and chest CT scans in the same year. Desperito evaluated the mammograms without the help of patients' prior exams or the additional imaging tests that women normally get when there are questions about their mammograms. "We practically tied her hands and blindfolded her," Salvatore says. "Just four standard views to look at and make the decision, should I biopsy anything on this patient, or should they come back in a year?"
Salvatore read the CT scans. Two years later, they compared their results with the patients' actual outcomes and found that the chest CT scans diagnosed breast cancer with 98 percent accuracy. "The sensitivity and specificity for CT was amazing," says Salvatore. "It was better than mammography, but I wasn't trying to be better. I just wanted to see if it was good."
A New Cancer Screening Tool
There is currently no official use for CT in breast imaging. Because mammography uses radiation to produce images, radiologists turn to exams that don't subject patients to more radiation—such as ultrasound and MRI—to supplement mammograms.
But Salvatore suggests that breast imaging has been slow to catch up with recent developments in CT imaging. CT didn't exist in the early days of mammography, when studies in the 1960's showed that mammograms could detect breast cancer early enough to save lives. In 1976, when mammography was officially recommended as a screening tool by the American Cancer Society, CT had been in widespread use for less than five years.
A CT image is made up of a series of "slices", which radiologists put together to get a three-dimensional view of the body's tissues and structures. At a thickness of 10 millimeters, early CT slices were crude, and the radiation dose it took to get the images was high. Today, CT slices are a half millimeter which has led to more precise imaging and consequently, more widespread use as a diagnostic tool. But the biggest development in CT imaging, Salvatore says, has to do with the radiation dose. A CT scanner can now obtain images using a very low dose of radiation—comparable to that of a mammogram.
"The combination between thin slice and low dose makes CT a contender for diagnosing breast cancer," says Salvatore. "It could be a valuable tool."
In fact, the development of "low-dose CT" (LDCT) led to a 2013 recommendation by the United States Preventative Services Task Force (USPSTF) that CT be used as a screening tool for lung cancer.
One of the reasons that CT has been understudied in breast imaging has to do with common protocols which encourage both technologists and radiologists to ignore the breasts on a CT scan. Most of the time, women are asked to remove their bra for a CT scan, causing the breasts to fall to the side. Then, the technologist creates a "window" which inadvertently excludes the parts of the breasts where cancer is most commonly found. Chest radiologists are also trained to ignore the breasts, to save time and confusion. "A woman is getting radiation and we're not even giving ourselves the chance to find a two-centimeter cancer," Desperito says.
At Columbia and NewYork-Presbyterian, Salvatore has already made changes to CT protocols which increase the chances of a radiologist finding a breast cancer. Now, women are asked to keep their bras on for a chest CT, and technologists are instructed to include at least one series of slices where the breasts are in full view. Salvatore points to a 2014 study in which a group of physicists determined that when the breasts are in front rather than to the side, radiation to the breast actually decreases.
A Challenging Exam
Both Salvatore and Desperito point to the many challenges posed by mammography as the most compelling reason to explore a possible alternative. When used regularly, mammography actually works very well; studies have shown that women who get annual mammograms starting at age 40 reduce their chances of dying of breast cancer by 40 percent.
But achieving that kind of risk reduction for women worldwide is virtually impossible with mammograms alone, Desperito says, because mammography requires specialized equipment along with technologists and radiologists who are trained in breast imaging. In lower- and middle-income countries (LMCs), the availability of mammography varies widely and often isn't an option at all. CT, on the other hand, is already widely in use around the world.
Both radiologists point out that for many women, discomfort is another obstacle to scheduling annual mammograms. A good mammogram depends on compressing the breast as much as possible while images are made. For most women, compression is uncomfortable and sometimes painful. The discomfort is compounded for women who have breast implants, which require a skilled technologist to image safely.
A third challenge is the recall rate associated with mammography. Between 10 and 14 percent of women who have mammograms are called back for additional screening, for reasons which range from a blurry image to a finding that needs further examination with ultrasound or other tests. For women who work or have childcare duties, callbacks can pose enormous challenges.
All of these obstacles, Salvatore argues, disappear when you look at the breasts on CT. "The beauty of CT is that it takes less than a minute. There's no compression. And I don't need them to come back for additional imaging. CT can determine whether a nodule is cystic or solid."
A Role for CT in Breast Cancer Screening
Before she was a radiologist at CUIMC, Salvatore was involved in several other studies which suggest that CT could be considered as a screening tool for breast cancer. In a retrospective study published in Radiology in 2014—while she was a radiologist at Mount Sinai Hospital—Salvatore and her colleagues found that CT performed as well as mammography when looking at breast density, a key risk factor for breast cancer.
In a more recent study published in Translational Lung Cancer Research, Salvatore collaborated with the Mount Sinai team to look at the added benefit of early detection of other diseases with lung cancer screening. They showed a reduction in mortality for lung cancer by 20 percent with lung cancer screening, but also a reduction of mortality from all causes by eight percent. "So I would expect that with CT we would decrease mortality not only from breast cancer but also decrease mortality from cancer from other regions," Salvatore says.
She is applying for grants to conduct a prospective trial in which volunteers come in for a CT and mammogram on the same day, and she and Desperito will evaluate them separately. This will help eliminate the biases of the retrospective study, in which the population they looked at had health conditions which led to the CT. "I just want to make sure we look, because from my vantage point as a mammographer and a chest radiologist, I can see that it's easier to diagnose breast cancer on a CT most of the time," she says.
Desperito, who has been looking at mammograms for her entire career, can see immediate uses worldwide if the research continues to show advantages of CT as a method for detecting breast cancer. In countries and areas that don't have access to mammography, she explains, women get diagnosed at a later stage and are more likely to die from breast cancer. She believes that CT could address this disparity, both in the U.S. and internationally. "Especially in rural areas, there's just so much more access to CT," she says.
In 2021, the USPSTF changed lung cancer screening recommendations to include people who are younger and smoked fewer cigarettes than those included in previous guidelines. This presents an even more immediate opportunity, Desperito says.
"What if women coming in for lung cancer screening could have their breast tissue evaluated as well, so that they don't need both a CT and a mammogram every year?" Desperito says. "Let's just start with that population."
One thing she can say for sure is that women would be more likely to come for an exam that doesn't involve compression. "Maybe this is a better way to take care of women," she adds. "We need to figure that out."