With screening guidelines and financial coverage varying among health systems and insurers the model of the Dana-Farber Cancer Institute in Boston provides quantitative predictions of the mortality benefits, on average, in populations of women over the course of 40 years.

"We're not advocating any particular interval for mammography screening," says Sandra Lee, ScD, a biostatistician at Dana-Farber who developed the model along with Marvin Zelen, PhD, of Dana-Farber and the Harvard School of Public Health. "This is a preliminary tool to show policymakers the kind of information they can draw on to help them make decisions."

The mathematical tool generates comparative information that's impossible to obtain in the real world, say the scientists, because clinical trials would require hundreds of thousands of volunteers following a variety of schedules over many years to demonstrate small mortality differences - and would be prohibitively expensive. Moreover, adds Lee, such trials would be ethically questionable because of the need for unscreened control groups.

At present, American Cancer Society guidelines recommend that women age 40 and older have a screening mammogram every year and that they "should continue to do so for as long as they are in good health."

But payers differ in their coverage for the tests: In Great Britain, said Zelen, the National Health System pays for mammograms only at three-year intervals and doesn't cover any screening whatsoever for women younger than 50, when the incidence of breast cancer is lower and mammograms are effective.

"It's clear that the more mammograms you give, the more able you are to locate disease that a person didn't know about," Zelen says. But, testing with increasing frequency has diminishing returns, while boosting the odds of "false positives" that can be traumatic to women and lead to unneeded biopsies that drive up health costs.

MEDICA.de; Source: Dana-Farber Cancer Institute