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I'm Rob Logan, Ph.D. senior staff National Library of Medicine substituting this week for Donald Lindberg, M.D, the Director of the U.S. National of Medicine.

Here is what's new this week in MedlinePlus.

To listen to Dr. Lindberg's comments, click here

A recent Norwegian study found breast cancer occasionally seems to disappear on its own without medical intervention. The study and an accompanying editorial, published in the Archives of Internal Medicine, present important findings and implications for breast cancer screening and treatment.

Turning first to the findings, the Norwegian study found 22 percent more breast cancer cases in a group of women who received mammogram screenings every two years -- compared to a similarly sized control group that received just one screening.

Specifically, 1,909 invasive breast cancer cases occurred among every 100,000 women who received biennial mammograms. Among every 100,000 participants who were screened once in six years, 1,564 women were diagnosed with invasive breast cancer.

So, the study found statistically significantly less cases of breast cancer during a six year period among the women who received one mammogram instead of three.

Since the number of invasive breast cancer cases should have been similar, and other explanations (such as differentiating risk factors), were ruled out by the study's methods, the authors suggest the possibility that some invasive breast cancer (that otherwise would have been detected) was not present after six years because it disappeared naturally. The authors use the term 'spontaneously regress' to describe cancer that disappears on its own.

The participants in the Norwegian study were women between ages 50-64. More than three of every four women in both groups of the Norwegian study commendably received a mammogram (upon request) by the study's three person team (that includes a Norwegian epidemiologist and pathologist and an American physician from the Dartmouth Institute of Health Policy and Clinical Practice).

An editorial that accompanied the Norwegian study implies this is the most compelling evidence ever found that cancer occasionally disappears on its own.

The editorial added the study was not a randomized control trial. However, the authors note future placebo-controlled randomized trials to explore spontaneous remission are unlikely --because inaction is not an ethical option in conducting breast cancer clinical trials.

Otherwise, the editorial notes the Norwegian study meets rigorous research criteria, including a high number of participants, a high percentage of women screened, and an exacting accounting of breast cancer cases from the Norwegian Cancer Registry.

The National Cancer Institute estimates about 40,000 women and 450 men will die from breast cancer in the U.S. this year. Breast cancer is the second leading cause of cancer deaths among adult American women. A mammography is a special type of X-ray of the breast and is a widely used screening tool to detect breast cancer.

Among the study's implications, the study's authors explained their findings do not suggest that mammograms cause, or are linked, to invasive breast cancer.

Second, the authors noted that breast cancer screening programs and early cancer detection programs remain important for women even if an unknown number of breast cancers may disappear on their own. Instead, the issue is whether mammograms lead to the treatment of breast cancer that otherwise would disappear.

Third, the authors of the editorial explain there is no definitive scientific explanation why some breast cancers disappear, some are contained, or some unfortunately spread (or metastasize) throughout the body. One reason is the underlying understanding about how cancer progresses remains unknown. Similarly, the reasons why cancer seems to disappear in some women will remain a mystery until breast cancer's underlying biological mechanisms are better understood.

Nevertheless, some public health officials are concerned the Norwegian study's results will confuse women about the safety and efficacy of mammogram screenings. A leading cancer screening official told the New York Times that the study's interpretation about spontaneous remission was too simplistic. Others worried that the misinterpretation of the study could undo recent progress in reducing breast cancer deaths because of screening and early detection.

Conversely, the accompanying editorial reminds us that the  Norwegian study identifies new research areas that someday may illuminate why breast cancer emerges, sometimes is contained, at times spreads through the body, and occasionally disappears.

While the current uncertainty persists, MedlinePlus.gov contains separate, health topic pages about mammography and breast cancer. MedlinePlus.gov's breast cancer health topic page is especially comprehensive and contains an entire section on prevention/screening, along with overviews, the latest news, and information on diagnosis/symptoms, treatment and disease management, plus helpful issues, such as coping with breast cancer.

To find MedlinePlus.gov's breast cancer health topic page, type 'breast cancer' in the search box on MedlinePlus.gov's home page. Then, click on 'Breast cancer (National Library of Medicine).'

MedlinePlus.gov's mammography health topic page contains an interactive tutorial (in English and Spanish) with spoken narration and easy-to-understand terms. There is additional information on related issues, such as breast feeding and mammography, and comparative breast imaging approaches. The page includes links to current mammography clinical trials and other research findings.

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