Gov. Jerry Brown stirred debate recently when he vetoed a California bill that would require doctors to notify women if they have dense breast tissue — which could obscure detection of cancer on a  mammogram.  Doctors would also be obligated to inform such patients that they might benefit from further diagnostic testing, such as an ultrasound.

Although Connecticut and Texas have passed similar bills and several others are pending in half a dozen other states,  Brown was uncomfortable with the language of  SB 791, noting in his veto message:

“Such a notice must be more carefully crafted, with words that educate more than they prescribe.”  Brown suggested that SB 791, proposed by state Sen. Joe Simitian, a Democrat from Palo Alto, could create “ unnecessary anxiety” in patients.

ABC News reported on the issue earlier this week, noting that interest and legislation had come to the fore in large part because of lobbying by the nonprofit organization Are You Dense, which was founded to increase awareness about breast density, a  cancer risk factor that, according to documents accompanying SB 791, 95 percent of women over the age of 40 don’t know about.

The group has met with much opposition from doctors and state medical institutions. In the case of the recent veto, the California State Medical Association lobbied against the bill, citing the increased medical costs and increased — and unnecessary — anxiety it would produce among patients who are told they might need additional testing.

Is there medical justification for such a requirement? ABC News asked docs to weigh in on the pros and cons of requiring doctors to disclose information about breast density and further breast cancer screening.

“Fat on a mammogram is black and the other structures [such as connective tissue] are gray and white.  Cancers are also gray and white, so that they can sometimes be hidden by the normal non-fatty [dense] tissues,” explains Dr. Daniel Kopans, a professor of radiology at Harvard Medical School.

While some have said that women with dense breasts (those with a large amount of nonfatty tissue) they are four to five times more likely to develop breast cancer than women with low breast density, acording to the Susan G. Komen for the Cure.

 Kopans says that this might not be true.

“Women with dense breast tissue are at slightly increased risk of developing breast cancer, but it is not the major risk that some have suggested. Almost all women (85 percent) in their 30s have dense breast tissue, and yet they are at relatively low risk of developing breast cancer (the risk of breast cancer increases with increasing age),” he says. 

Kopans believes that women shouldn’t be referred  for further testing just because they have dense breast tissue until more research can find that this actually saves lives. He worries that increased screening with ultrasounds will only lead to more false positives.

Other physicians, however, believe that increased knowledge on the part of the patient could only benefit.

“Women with dense breast tissue … should be aware of the increased risk,” says Dr. Kristin Byrne, chief of breast imaging at Lenox Hill Hospital in New York City. “I have not found this creates unnecessary anxiety… Patients are thankful to have the ultrasound.”

Dr. Gary Lyman,  director of the Comparative Effectiveness and Outcomes Research Program at Duke University School of Medicine, said that women should know, but that it might not change how they are screened for breast cancer.

“Personally, I believe that clinicians should tell women if they have dense breasts, as the sensitivity of conventional screening methods is lower in these settings,” he says. “While I support informing women if they have dense breasts, there are few concrete recommendations for breast cancer screening other than increased awareness and attentiveness to changes in the breast.”

Other doctors echoed the “more is not better” warning when it comes to upping the amount of breast cancer screening that women should undergo.

“There are no randomized controlled trials completed that demonstrate a reduction in mortality from breast cancer for supplemental screening — as there are for mammography, and in most regions of the USA, supplemental screening is not covered by medical insurance, making it effectively available only to the wealthy or the very concerned,” says Dr. Edward Sickles, section chief of breast imaging at the University of California, San Francisco.