Routine breast screening with mammograms is less effective at preventing cancer deaths than expected, Norwegian researchers said on Wednesday in a study that reignites a fierce debate over the value of screening.

They said inviting women aged 50 to 69 to have routine mammograms and offering them better care from a team of experts helped cut the breast cancer death rate by 10 percent.

But the death rate in women over 70 - a group that also got better care but were not urged to have mammograms - fell by 8 percent, indicating that the mammograms only produced a slight benefit.

“There is a reduction in mortality, but it’s lower than we anticipated,” Dr. Mette Kalager of Oslo University Hospital, whose study appears in the New England Journal of Medicine, said in a telephone interview.

The researchers had expected a 30 percent reduction.

Based on the study, screening mammograms may add only a 2 percent benefit in cutting breast cancer deaths, Dr. Gilbert Welch of New Hampshire’s Dartmouth Medical School wrote in a commentary in the journal.

Welch said the new results show that for every 2,500 women age 50 who receive a mammogram, only one will avoid dying of breast cancer and as many as 1,000 will be told that doctors have seen something suspicious.

About 500 of those will be subjected to a biopsy, and between 5 and 15 women will be treated unnecessarily for a condition that was never going to bother them, Welch wrote.

DEBATE REIGNITED

The study adds fresh fuel to the debate over the effectiveness of routine mammograms, billed as a way to detect a cancer that kills 519,000 people worldwide a year.

In November, new guidelines from the U.S. Preventive Services Task Force - recommending that the test be taken every other year instead of every year for women 50 to 74 - sparked criticism from many breast cancer experts, advocacy groups and U.S. lawmakers.

The Norwegian findings prompted questions from Dr. Daniel Kopans of Massachusetts General Hospital and an official with the American College of Radiology.

“This article suggests that most of the decrease in breast cancer deaths is due to improvements in therapy with a lesser contribution from screening,” he said in a statement.

“There are large, published studies from Sweden and the Netherlands that show that most of the decrease in deaths is actually due to screening and not therapy,” Kopans said.

Kalager and Welch said those studies were done before 1990 and screening may be less effective now because treatment has improved.

Kalager and her team studied data from 40,075 women, tracking the reduction in cancer deaths as a screening program was expanded throughout Norway, beginning in 1996. It also coincided with improved treatment for patients.

One of the study’s authors, Marvin Zelen of Harvard, said in a telephone interview that the women studied had access to a multidisciplinary team to manage their disease. That makes it harder to discern which element - mammograms or therapy- played the bigger role in cutting cancer deaths by 10 percent.

Kopans said the average follow-up of just 2.2 years was too short and likely accounts for the new results. “The full impact of screening would not be expected so soon,” he said.

Kopans also said the women in the Kalager study were screened every two years, whereas women in the United States have been encouraged to be screened every year, which would give cancers less time to grow between screens.

Kopans said the debate over mammograms “is confusing and draining” for women and their doctors.

“It is time to accept that screening, beginning at the age of 40, is saving tens of thousands of lives,” he said.

SOURCE:  New England Journal of Medicine, online September 23, 2010.