Reuters/Rhoda Baer/National Cancer Institute

The number of breast cancers suffered by American women will increase by about 50 percent by 2030, researchers from the National Cancer Institute reported Monday.

Breast cancers already are the most common form of cancer in the United States, with 283,000 diagnosed cases in 2011. That number is predicted to rise to about 441,000 in 2030, according to Philip Rosenberg, a senior investigator in the division of cancer epidemiology and genetics at the National Cancer Institute. The information was released at the annual meeting of the American Association for Cancer Research.

Currently, one in eight women will develop breast cancer in her lifetime, Rosenberg said at a news conference Monday morning.

In a more optimistic development, Rosenberg forecast a decline in the number of breast cancers that are not receptive to estrogen, known as ER-negative tumors, which are more difficult to treat because they do not respond to endocrine therapy. They are expected to decline from about 17 percent of all tumors to about 9 percent, for reasons that are not clear, the researchers reported.

Rosenberg said the predicted increase in breast cancers reflects three trends: The increasing number of older women in the population as the Baby Boom generation ages; increased life expectancy that allows more women to develop breast cancer at some time in their lives; and a clear rise in the number of tumors receptive to the hormone estrogen (known as ER-positive breast cancers). The last trend is probably the result of changes in "circumstances and lifestyles," he said, but the research model looked at total numbers, not causes, he said.

[3-D mammography substantially improves screening for breast cancer, study shows]

However, there is controversy in this field over the role of mammography and the definition of some kinds of breast cancer. Last July, a panel of the National Cancer Institute concluded that improved screening has resulted in the over-diagnosis and over-treatment of cancers that are not life-threatening, without significantly reducing the death rate from the disease.

Some experts also believe the time has come to stop considering "ductile carcinoma in situ"--the presence of abnormal cells in the milk ducts of the breast--as a cancer, because the disease is not invasive and does not threaten women's lives if left untreated. Yet because of the term "cancer," women sometimes choose mastectomies when they receive the diagnosis.

“Right now, we have women getting bilateral mastectomies for ductal carcinoma in situ, which is not a cancer,” Otis Brawley, chief medical officer of the American Cancer Society, said at the time. “It’s the world turned upside down.”

[Experts warn of dangers of overdiagnosis and treatment of cancer]

Also Monday, the U.S. Preventive Services Task Force updated its recommendations on screening for breast cancer but made virtually no changes to its 2009 guidelines. As it did six years ago, the panel suggested that women between the ages of 50 and 74 should have mammograms every two years. In particular, women aged 60 to 69 are most likely to avoid death from breast cancer through such screenings, according to the panel, a volunteer group of experts on preventive and evidence-based medicine.

The influential task force gave a “B” grade to that recommendation, meaning that there is a good chance of moderate to substantial benefit to women who follow it.

On the more controversial question of beginning mammography for women between 40 and 49 years old, the task force again said that the decision should be made case by case by a woman and her doctor. While mammography for this age group may result in a small number of averted deaths, the practice also raises the risk of over-diagnosis — including unnecessary biopsies — and over-treatment for women with conditions that do not threaten their health.

The panel clarified its “C” grade by explaining that it denotes “moderate certainty of a small net benefit in the population” and noted that women in this age group with a parent, sibling or child who has breast cancer may benefit more than the average woman.

The American Cancer Society and the American College of Obstetricians and Gynecologists recommend a more aggressive screening regimen, suggesting that women receive regular mammograms beginning at age 40.

The task force also concluded that there is not enough evidence to assess mammography for women 75 or older, the effectiveness of 3-D mammography or the benefits of extra screenings for women with dense breast tissue.

The recommendations are drafts that will be subject to public comment and other forms of feedback before they are finalized.

Correction: This post originally said that the National Cancer Institute is one the agencies that recommends women receive regular mammograms beginning at age 40. As a research agency, the institute makes no medical recommendations.