Researchers from the National Cancer Institute have found that mammography rates are on the slide across the United States, raising concerns in health experts that more women eventually will be diagnosed with breast cancer that is more difficult to treat.

The American Cancer Society recommends that women undergo regular mammograms at age 40, yet studies such as this one show a decline in the screening rate which translate into higher breast cancer death rates.

"That's the thing we worry about the most," said lead researcher Nancy Breen, PhD, of the National Cancer Institute. "Women who weren't diagnosed early because they didn't get their on-schedule mammogram might be diagnosed later with a later stage of cancer."

For this study, Breen and colleagues reviewed data from the National Health Interview Survey, a yearly survey that interviews around 35,000 people across the United States. The data showed that while mammography use went up from 1987 and 2000, between 2000 and 2003 rates stayed about the same. But by 2005, mammography rates for women overall had dropped to about 66 percent from 70 percent in 2000. Breen calls this trend "disturbing." 

The decline was seen across all subgroups, even those that have traditionally adhered the most to mammography screening recommendations. 

The study cites a few possible reasons for the decline in usage, such as a drop in the number of insured women; spikes in mammogram co-pays; questions regarding mammogram effectiveness; or less pronounced fear of breast cancer.

However, Breen feels that the cause is likely a combination of many factors.

"We really need to know why it is that screening isn't happening before we can talk about developing strategies that are going to work [to raise levels again]," she said. "We can't assume that people who have been screening will continue to screen, and we need to continue to make it clear that this is of benefit to them," she says.

The survey results were published in the online edition of the journal Cancer.