Mammography provides equal benefits to women in their 40s

June 1, 1998

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, report researchers from the University of Chicago Medical Center in the June 1, 1998 issue of Cancer.

Cancers detected--at any age--by screening mammogram 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, MD, PhD, professor of radiation and cellular oncology at the University of Chicago 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 adds.

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 ages 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," explained Heimann, "the disease appears to be more aggressive in younger women. 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--Dr. Heimann and University of Chicago colleagues Jeffrey Bradley, MD, and Samuel Hellman, MD--followed 869 cases of women with Stage-I or Stage-II breast cancer who received breast-conserving therapy (BCT) at the University of Chicago Hospitals between 1984 and 1994. (BCT included lumpectomy and local radiation. Most node-positive patients also received chemotherapy, and about 40 percent received tamoxifen to prevent recurrence.)

Tumors detected by mammogram were virtually identical--whether women were in their 40s or older--with similar average size and grade, also 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 (2 cm versus 1.5 cm), of a higher grade (36 percent grade-3 versus 25 percent), and more likely to have spread to axillary lymph nodes (31 percent versus 20 percent). 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 Dr. 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," concludes Dr. Heimann, "but a prudent choice."

Breast cancer is the leading cause of cancer death in women age 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 older than age 65, it rises to 450.

Summary:
Women should get annual mammograms after age 40. The benefit of detecting breast cancer early is greater for younger women, who progress more rapidly to more aggressive disease--with worse outcomes--than older women, report researchers from the University of Chicago in the June 1, 1998 issue of Cancer.

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