BEIJING, March 28 (Xinhuanet) -- New American Cancer Society guidelines say women at high risk for breast cancer should be screened with MRI in addition to mammograms.

    Top researchers also advised Tuesday that anyone recently diagnosed with cancer in one breast should have magnetic resonance imaging to make sure the other breast is tumor free. Their study, published in the New England Journal of Medicine, found more than 3 percent of new breast cancer patients had cancer in the other breast that standard mammograms and physical examination missed.

    The two developments are the latest steps in the evolution of medical thinking about the use of MRI -- a sophisticated and expensive tool -- to find breast tumors. But experts caution healthy women at low or average risk should continue to rely on mammography and physical exams to detect signs of cancer.

    Widespread use of MRI, they note, could detect non-threatening cancers that don't need to be treated and therefore might do more harm than good.

    "Finding more cancers is not necessarily a good thing," said Dr. Steven Woloshin of Dartmouth Medical School. "The key is whether these 'missed cancers' are ones that were destined to cause problems, and whether earlier detection and treatment has a net benefit. These issues can only be resolved with a randomized trial."

    Even for women diagnosed with invasive breast cancer on the basis of conventional tests, MRI can be a double-edged sword.

    Findings of additional tumor sites can affect the patient's emotional state and may lead to unnecessary mastectomies, said Dr. Nora Hansen, director of the Lynn Sage Comprehensive Breast Center at Northwestern Memorial Hospital.

    "Patients freak out," she said. "They have this knee-jerk reaction -- 'I just want everything taken out.'"

    The cancer society says women at high risk will benefit from the addition of MRI to their regular screening tests because MRI is more sensitive and finds smaller tumors compared to mammography.

    The new guidelines recommend that all women whose lifetime risk of breast cancer is around 20 percent or higher get an annual MRI. A 60-year-old white woman with no children and two close relatives with breast cancer has a 23 percent chance of being diagnosed before her 90th birthday. The average American woman's lifetime risk is 13 percent.

    Women who automatically fit into the high-risk category include those with a genetic mutation that predisposes to breast cancer, such as BRCA carriers.

    The society said evidence was insufficient to recommend for or against MRI screening in women with a personal history of breast cancer or precancerous conditions. But its recommendations were written before the latest study was completed.

    That study looked at 969 women recently diagnosed with cancer in one breast but not the other. All were given MRIs of the second breast, which found possible cancer in 121 women. Biopsies confirmed invasive cancer in 18 of them.

    "This study is pretty definitive evidence that the opposite breast needs to be evaluated with MRI," said study author Dr. Etta Pisano of the University of North Carolina.

    (Agencies)