The US Preventive Services Task Force (USPSTF) recommends that women undergo screening mammography every one to two years beginning at age 40.

After an extensive review of published studies, the task force concluded that screening at this frequency can reduce deaths from breast cancer, although the report noted that evidence for a survival benefit is "strongest for women aged 50 to 69."

The task force gives the recommendation only a "B" grade — meaning that there is "fair evidence" to recommend mammography screening every one to two years for women 40 and older.

And the USPSTF reported that there is not enough evidence to recommend for or against either annual clinical breast exam (CBE, a breast exam by a physician) or breast self-examination (BSE) as a means of reducing breast cancer mortality.

With these new guidelines, the "task force recommendations are now more similar to the American Cancer Society recommendations for breast cancer screening," said Robert Smith, PhD, who is director of cancer screening for the ACS.

Currently the American Cancer Society recommends annual mammography screening beginning at age 40. Moreover, it recommends monthly breast self-examination beginning at age 20 and clinical breast examination every three years from age 20 to 39, then yearly thereafter.

Smith noted that the USPSTF uses very strict criteria when assessing the results of studies. Those criteria make it difficult to provide concrete proof that clinical breast exam and breast self exam are worthwhile examinations, or that annual screening offers a measurable benefit over screening every two years for women in their 40s.

But, he added that the available data strongly support the notion that annual mammography is the most effective way to detect fast-growing tumors in younger women (age 40 to 49). Because tumors grow faster in this age group, and because their breasts are more dense, annual screening is important. Small lumps are difficult to detect with only self examination or clinical examination.

The new USPSTF guidelines are published in the Sept. 3 issue of Annals of Internal Medicine (Vol. 137, No. 5), which also includes a summary of the evidence that the task force used in arriving at the new guidelines (p. 347), a new report from the Canadian National Breast Screening Study (p. 305), which is one of the studies reviewed by the USPSTF, and two editorials (pp. 361; 363) that discuss the new guidelines.

Linda L. Humphrey, MD, PhD, lead author of the evidence summary, said the "recommendation is grade B because the evidence is imperfect. The studies aren't the highest quality and so the evidence is not as black and white as we would like."

Humphrey said that the USPSTF based its recommendations on a meta-analysis of data from eight studies, seven of which included women aged 40 to 49. And six of those seven studies were not designed to evaluate the ability of mammography screening to reduce breast cancer mortality in these younger women.

With such a mixed bag of results, the USPSTF could do no more than issue a qualified endorsement of screening for younger women, said Humphrey. "But from a personal perspective, I would recommend screening," she said.

Anthony B. Miller, MB, FRCP, is the lead investigator of one of the largest studies analyzed by the USPSTF — the Canadian National Breast Screening Study-1 (CNBSS-1). He was critical of the task force recommendations, although he said he has not yet had time to review the evidence summary by Humphrey and her colleagues.

Miller, who is a consultant to the World Health Organization and head of the division of clinical epidemiology at the German National Cancer Institute, said the latest findings from the CNBSS-1 included an average of 13 years of follow-up that "confirm no survival benefit for mammography screening in younger women."

The latest CNBSS-1 report, which is also published in Annals, found 105 breast cancer deaths among women who had annual mammography for four or five years, and 108 breast cancer deaths among women who were followed with "usual care," meaning clinical breast examinations and mammography when a suspicious lump was detected.

The USPSTF rated this study near the top in terms of quality among those analyzed in making its recommendations. However, this study, along with all of the others analyzed, was still found to have "important methodologic limitations."

That being said, Miller contended that there is no evidence that screening mammography in women younger than 50 can reduce mortality by 20% or more, which he regards as the threshold to prove that mammography is beneficial.

Otis Brawley, MD, a professor of oncology and epidemiology at Emory University School of Medicine in Atlanta, said the ongoing debate can be confusing for both women and their doctors.

"My view is that the benefits of screening have been exaggerated by some people and some groups, but that doesn't mean there is no benefit to screening," he said.

Brawley agreed with the USPSTF assessment that "all these studies have problems or flaws," but he said that he believes the overall weight of the evidence shows that "screening saves lives." In addition, he said that while it is undeniable that the risk for breast cancer increases with age, it is very difficult to draw a line in the sand at age 50.

"What makes a 50-year-old woman so different from a 46- or 47-year-old woman? In many cases I would argue that they are biologically very similar," he said. The bottom line, he said, "is that I don't see the harm in screening a woman who is in her 40s."

However, Steven N. Goodman, MD, PhD, an epidemiologist at the Kimmel Cancer Center, Johns Hopkins University in Baltimore, said that there might be some harm associated with mammography. Specifically, Goodman said "mammography is associated with excess surgery. I don't mean just excess biopsies but an actual excess numbers of lumpectomies and mastectomies."

Goodman wrote one of two editorials that were published along with the USPSTF guidelines and the Canadian study results. He said that mammography often detects ductal carcinoma in situ (DCIS), which is a type of early breast cancer for which surgical treatment remains controversial. Without mammography, some cases of DCIS probably go undetected throughout women's lives, and are discovered only at autopsy.

Even when they don’t lead to such surgeries, Goodman said that mammograms sometimes give false positive findings, which then subject the patient to additional testing and increased anxiety.

Harold Sox, MD, the editor of Annals, wrote the other editorial, which suggested that the debate concerning screening mammography is far from over. Sox said he thinks "the recommendations for women over age 50 are going to provide some reassurance that this expert group has evaluated the evidence and thinks that screening has a beneficial effect on breast cancer mortality, albeit a relatively modest one."

But, he said that the evidence to support screening for women younger than 50 is still controversial, although many younger women continue to believe that screening is effective for them.

Smith agreed that women do need adequate counseling about the benefits and limitations of screening, but he said in the final analysis, he thinks mammography is the right choice for women 40 and older.

But he said the lingering discussion about screening women in their 40s is that some individuals continue to insist that it is contoversial rather than evaluate the totality of the data.

"The US Preventive Services Task Force is quite conservative in their evaluation of the data and have clearly pointed out that the strength of the evidence has more to do with the way these studies were originally designed than any real doubts about whether or not screening can be beneficial to this group," Smith said. "That conclusion based on scientific evidence is the more credible message."