June 11, 1998
Vol. 17, No. 18

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    University study urges annual mammograms after age 40

    By John Easton
    Medical Center Public Affairs

    Although breast cancer is more common after age 50, the benefit of detecting breast cancer through an annual screening mammogram is greater for a woman in her 40s than for an older woman, University researchers report in the June 1 issue of the journal Cancer.

    Cancers detected at any age by screening mammograms tend to be equally small, averaging about one centimeter in diameter. But for women in their 40s, cancers first noticed not on a mammogram but as a palpable lump tend to be larger, more aggressive, and more likely to have already spread to the nearby lymph nodes than for older women.

    Consequently, "more older women benefit from mammography, but the younger women who benefit from mammography benefit more," said Ruth Heimann, Assistant Professor in Radiation & Cellular Oncology and director of the study. "Women under 50 with clinically rather than mammographically detected cancers have worse disease and worse outcomes than women over 50."

    This finding "tips the scales, already leaning that way, a few more notches in favor of annual screening mammograms for women in their 40s," she added. For women with breast cancers detected via screening mammograms, 90 to 92 percent -- nine out of 10 -- were alive and cancer-free five years later. For women 50 and older, with cancers detected on a clinical exam rather than by mammogram, disease-free survival fell only slightly, to 87 percent.

    But for women 40 to 49 with breast cancers detected as lumps, five-year disease-free survival plunged to 77 percent -- about three out of four. "Given time to grow big enough to be felt, the disease appears to be more aggressive in younger women," Heimann said. "Breast tumors in women under 50 grow faster, establish their own blood supply more quickly, and are more likely to spread not just to nearby lymph nodes but to distant sites, making treatment more onerous and less effective."

    The researchers -- Heimann and colleagues Jeffrey Bradley, Resident in Radiation & Cell Oncology, and Samuel Hellman, the A.N. Pritzker Distinguished Service Professor in Radiation and Cell Oncology -- followed 869 cases of women with Stage I or Stage II breast cancer who received breast-conserving therapy at the University of Chicago Hospitals between 1984 and 1994.

    Tumors detected by mammogram were virtually identical, whether women were in their 40s or older, with similar average size and grade, and similar rates of lymph-node spread and disease-free survival.

    Tumors detected by clinical exam, however, were significantly more advanced for younger women. They were 33 percent larger, of a higher grade and more likely to have spread to axillary lymph nodes. With more advanced disease, survival rates decrease.

    While critics of mammograms for younger women have emphasized the greater difficulty of detecting smaller tumors in the denser breasts of younger women, this study indicates that the principal alternative method for early detection, breast palpation, is also less effective in denser, pre-menopausal breasts.

    "Although our data do not address the public policy or cost-effectiveness considerations of screening mammograms for women under 50, they do indicate that the benefit of mammography is not limited to older women," said Heimann.

    "Breast cancer may be 50 percent more common for women in their 50s than for those in their 40s, but our data suggest that the life-extending benefits of early detection are more than 50 percent greater for women who get breast cancer in their 40s."

    "From an individual young woman's point of view the clinical decision to get annual screening mammograms is no longer a 'toss up,' as some have suggested, but a prudent choice," Heimann said.

    Breast cancer is the leading cause of cancer death in women ages 35 to 54. For every 100,000 women in their 40s, 162 will be diagnosed with breast cancer. For women in their 50s, that rises to 251, and for women over 65, to 450.