For more than half of all women, annual screening mammograms might lead to one false-positive finding per decade, and digital mammography trumps film for women with dense breasts.

These were two of the findings of a pair of articles published Tuesday in the Annals of Internal Medicine that tackled some of the most controversial topics in mammography. The studies involved records for hundreds of thousands of women, and relied on the Breast Cancer Surveillance Consortium, the most comprehensive breast cancer registry in the world, according to the authors.

The researchers found that after a decade of undergoing yearly screening mammograms, starting at 40, 61 percent of women will receive one false-positive exam, and 7 to 9 percent will receive a false-positive biopsy. But, in a finding seen as partly backing a controversial U.S. Preventive Services Task Force 2009 recommendation, a scan every two years is linked with fewer false positives than an annual scan: only 41 percent of women getting a biannual scan received a false-positive result after 10 years.

In 2009, a U.S. Preventive Services Task Force panel advised women to begin screening mammograms later in life, and only once every two years, instead of annually, as in previous guidelines.

However, in the study, although the stage at which cancers were found wasn't significantly different between annual and biannual screens, there was a small, though not statistically meaningful, increase in the risks of finding cancers at a later stage when women received scans once every two years. The proportion of late-stage cancer diagnoses was 2 to 3 percentage points higher in the biannual group, the researchers said.

Researchers also used a similar data set to tackle a related controversy: whether digital mammograms were superior to film mammograms. In their research, also published in the same issue, they found that digital and film mammograms were similar for most women, except digital was more sensitive at picking up cancers in women with very dense breasts or with estrogen receptor-negative tumors.

"Women aged 40 to 49 years are more likely to have extremely dense breasts and estrogen receptor-negative tumors; if they are offered mammography screening, they may choose to undergo digital mammography to optimize cancer detection," the researchers wrote.

Digital had an 84 percent sensitivity for those with extremely dense breasts, compared with 68 percent sensitivity for film. For finding cancer in women with estrogen receptor-negative tumors, digital had 79 percent sensitivity versus 66 percent sensitivity for film.

Digital was also somewhat more sensitive for women in their 60s, about 90 percent sensitive versus 83 percent for film.

In a statement, Rebecca Hubbard, assistant investigator at Group Health Center for Health Studies in Seattle, and a co-author of the two papers, said the researchers undertook the studies so women better understood the risks of false positives.

"We hope that by helping women know what to expect in terms of false-positive results, they'll be less likely to experience anxiety when they are called back for a repeat screening or biopsy," she said.

The digital vs. film study looked at records for 329,000 women, aged 40 to 79, who underwent 231,000 digital mammograms and 638,000 film mammograms. The cumulative false-positive risk study looked at records for 170,000 women who had their first screening mammogram between 40 and 59, in the years 1994-2006, and another 4,500 with invasive breast cancer diagnosed between 1996 and 2006.

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