Cancer screening poses a quandary for women with dense breast tissue. They’re at elevated risk for breast cancer, but mammograms often miss tumors buried in dense breasts — and insurers often resist paying for additional scans that may help find the masses.
Now a large study comparing various types of scans has found that mammography enhanced with iodine-based dye can detect three times as many invasive cancers in dense breast tissue as ultrasound.
And so-called contrast-enhanced mammography can find tumors that are much smaller than those found by regular mammography. M.R.I.s are better at detecting more tumors than standard mammograms, the study found, but are considerably more expensive.
The scans were given to women with dense breast tissue who had already undergone mammograms that hadn’t turned up any abnormalities.
“Contrast-enhanced mammography needs to become standard of care for women with dense breasts,” if they are at high risk of developing breast cancer, said Dr. Fiona J. Gilbert, a professor of radiology at the University of Cambridge’s School of Clinical Medicine. She is lead author of the study, which was published Wednesday in The Lancet.
Tumors typically show up as white spots on mammograms, but dense breast tissue also appears white, obscuring the tumors.
“When you have lots of white normal breast tissue, it’s hard to see the white cancers,” Dr. Gilbert said. “But when you do the contrast, the cancers take up the iodine, and all you’re seeing is this cancer lighting up.”
A large Dutch study published in 2019 showed that M.R.I.s are more effective than standard mammography at finding tumors in dense breast tissue. The new study is the first randomized controlled clinical trial to compare M.R.I.s, ultrasounds and contrast-enhanced mammography in women with dense breast tissue.
JoAnn Pushkin, executive director of the educational group DenseBreast-info, said the study showed that contrast-enhanced mammograms could save lives. They not only found more tumors but detected them when they were small and had not yet spread to the lymph nodes.
“This means these cancers were found early enough that most were still contained within the breast,” Ms. Pushkin said. “These were tragedies averted. If they had not been found, they would have grown undetected until they were horror stories.”
But while contrast-enhanced mammography is available in some centers in the United States, its use for breast cancer screening has not been approved by the Food and Drug Administration. (It is more often used as a diagnostic tool after suspicious findings appear on a regular mammogram.)
Partly that’s because of concern over allergic reactions to the contrast agent, which are uncommon but can be severe, according to Dr. Wendie Berg, a professor of radiology at the University of Pittsburgh School of Medicine and chief scientific adviser to DenseBreast-info.
Dr. Gilbert, the study’s lead author, also cautioned that while extra imaging can lead to earlier detection in women with dense breasts, it may also increase overdiagnosis and overtreatment of a medical condition that may never become life-threatening if left alone.
Yet most of the tumors detected with the contrast-enhanced scans actually were invasive and potentially life-threatening, Dr. Berg said. These cancers show up more readily when dye is used.
Contrast-enhanced mammograms are more cost-effective than M.R.I. scans, and they could be made more widely available at existing mammography centers with staff training and sometimes technology upgrades, Ms. Pushkin said.
The new study, carried out at 10 screening sites in the United Kingdom between Oct. 18, 2019, and March 30, 2024, was the kind of trial considered the gold standard in medicine.
More than 9,000 women aged 50 to 70 who had dense breast tissue and normal mammograms were randomly assigned in roughly equal numbers to receive standard digital mammography, M.R.I.s, ultrasounds or contrast-enhanced mammography. About 6,305 completed the additional imaging tests.
M.R.I. scans turned up 17.4 cancers per 1,000 exams, while ultrasounds found only 4.2 cancers per 1,000 exams. Contrast-enhanced mammograms detected 19.2 cancers per 1,000 exams, but the difference between M.R.I. and contrast-enhanced mammography was not statistically significant.
Not all of the tumors were invasive. M.R.I.s revealed 15 invasive cancers per 1,000 exams, ultrasounds found 4.2 invasive cancers per 1,000 exams, and contrast-enhanced mammography detected 15.7 invasive cancers per 1,000 exams.
Most of the cancers were less than two centimeters in size, and had not spread to the lymph nodes.
Detecting cancers when they are smaller should lead to better outcomes, Dr. Gilbert and her colleagues said. But the grade of the cancer — a measure of its abnormality and thus aggressiveness — is also important.
The research did not follow the patients long enough to learn whether using contrast-enhanced mammography would ultimately reduce deaths.
There were adverse events associated with the use of iodine dye. Twenty-four patients who underwent contrast-enhanced mammograms had reactions, and three experienced so-called extravasation, in which the dye leaks out of blood vessels into adjacent tissue.
There were no adverse events associated with ultrasound, and there was one case of extravasation among the women who received M.R.I.s, in which contrast dye is sometimes used.
Among the trial participants whose cancer was discovered during a supplemental M.R.I. was Louise Duffield, 60, who lives in Ely, near Cambridge.
Ms. Duffield was invited to participate in the trial in 2023, after her regular mammogram screening showed that she had very dense breasts. When she came in for an extra M.R.I., the scan identified a small lump.
A biopsy determined that the tumor was Stage 0, or very early, and confined within the milk ducts. Ms. Duffield had surgery to remove the tumor six weeks later, by which time it had already grown larger than it had appeared on the scans, hospital officials said.
Because of the location of the tumor, Ms. Duffield would have had difficulty identifying it with a self-exam. And since the tumor was not detected during her regular mammogram, she would not have had to come in for another scan for at least three years, based on U.K. guidelines.
Ms. Duffield was treated with radiation and is now free of cancer. “The tumor was deep in the breast, so if I hadn’t been on the trial, it could have gone unnoticed for years,” Ms. Duffield said in a statement. “Without this research, I could have had a very different experience.”
Roni Caryn Rabin is a Times health reporter focused on maternal and child health, racial and economic disparities in health care, and the influence of money on medicine.
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