Physicians, acknowledging patients' right to information, warn that experts don't understand why most breasts have areas of dense glandular and connective tissue, much less what to do about it.
In a statement last year, the American College of Radiology listed the "possible harms and unintended consequences" of notification mandates: The assessment of breast density is subjective. Dense breasts are common and experts disagree about whether that alone warrants more imaging tests. Women may panic or feel falsely reassured by their density report. Ultrasound and MRI screening could add to the problems of false alarms, of detecting and treating trivial cancers.
The radiologists' group also warned that without insurance coverage, "there may be an unfortunate disparity between women who can afford to pay and those who cannot."
The American Cancer Society, which recommends MRIs only for women at high risk of breast cancer, is also leery. "We have a long history of laws being passed to regulate health care where politicians are trying to be seen as being helpful, and they've actually been harmful," said Otis Brawley, the society's chief medical officer. "Ten states still have laws saying insurance companies must pay for bone marrow transplants for breast cancer," although the awful regimen was proved inferior long ago.
Mammography remains a hot-button issue, despite studies showing it has cut breast cancer deaths, and federal regulation that has standardized screening practices. Indeed, any woman whose mammogram appears reassuring gets a standardized letter that points out breast X-rays miss some cancers.
One reason for the misses is that X-rays are mostly blocked by glandular and connective tissues but can penetrate fat. Looking for a clump of cancer cells in dense breasts is like looking for a golf ball in a snowbank.
Why some breasts are denser than others "is a very hot topic in radiology right now," said Debra Copit, director of breast imaging at Einstein Medical Center. "We're taught that dense tissue decreases with age, and fat replaces it. But I did a study of over 90,000 women . . . and that's not an absolute. Whatever you're born with kind of stays with you over time."
The American College of Radiology has a 1-to-4 density grading scale. But only 10 percent of women have extremely dense breasts, and 10 percent have fatty breasts. The remaining 80 percent have a mixture.
Often, the grade is in the eye of the beholder - the radiologist.
"One may call a woman dense while another does not," said University of Pennsylvania radiologist Despina Kontos, who is researching objective ways to measure density.
The nature of some cancers also defies X-rays. Lobular cancers, which begin in the milk-producing lobes and account for 10 percent of invasive breast cancers, do not show up on X-rays because the malignant cells grow in lines, not piles.
Pat Halpin-Murphy, president of the Pennsylvania Breast Cancer Coalition, is a survivor of lobular cancer who has championed Pennsylvania's bill. It has passed in the state Senate and could go to a House vote this month.
"One, it saves lives," Halpin-Murphy said of a breast density law. "Two, it may very well save money" by reducing the treatment needed.
Researchers say there are no studies to support such claims - another reason the rush to pass mandates is troubling.
In Connecticut, which requires insurance coverage for ultrasounds, a flood of ultrasound exams led to detection of three additional breast cancers for every 1,000 women screened, studies found. But the ultrasounds also led to a flood of false alarms and biopsies that found no cancers - far more than with mammography. "I see laws trying to fix something that is not fixable," said Brawley of the cancer society.