Regular mammography screening for women in their 40s leads to diagnosis of breast cancer at an earlier stage, possibly improving opportunities for more effective, less radical treatment options, according to researchers reporting in the Jan. 15 issue of the medical journal Cancer (Vol. 97: 352-358).

This report comes on the heels of anAnnals of Internal Medicine (Vol. 137, No. 10: 783-792) article reported in December on the benefit of mammograms for women over 75 years old.

According to study lead author Sandra Buseman, MD, and colleagues at the University of Colorado Health Sciences Center in Denver, nearly 25% of all breast cancer deaths occur in women who were diagnosed between ages 40 and 49.

Buseman said even though breast cancer incidence has increased over the past decade, breast cancer deaths have decreased. She said the brighter outlook for survival may be related to the "widespread adoption of mammography screening, in addition to improvements made in therapy."

However, even with growing evidence that supports screening for older women, "The effectiveness of screening mammography in reducing breast carcinoma mortality for women 40 to 49 years of age is still being debated," Buseman said.

In the newest study, Buseman looked at 247 women diagnosed with breast cancer between the ages of 42 and 49. While 105 of the women had received a mammogram in the two years before being diagnosed, 142 had not undergone screening.

Those who had been screened were 44% less likely to be diagnosed with a later stage of breast cancer compared with women who had not received regular mammograms.

"In this study, 58% of cancers were detected by mammography alone and these cancers were more likely to be diagnosed at an early stage," Buseman said.

The authors did not specifically look at survival in this study, however.

And, Buseman reported, "Even though we found significant differences in stages at diagnosis, we did not find significant differences in regard to treatment in the screened and unscreened groups.” This may be explained by the fact that stage II breast cancers, although classified as “late stage”, are treated similarly to early stage cancers, she explained.

Buseman also pointed out that the study did not address potentially harmful consequences of mammography among women in their 40s. The test is less accurate in younger women, and in some cases, noninvasive (in situ) cancers might be treated more aggressively than is necessary.

The American Cancer Society estimates that in 2003 about 211,300 new cases of invasive breast cancer (stages I to IV) will be diagnosed among women in the US.. Carcinoma in situ (CIS) will account for an additional 55,700 new cases this year. CIS (stage 0) is noninvasive and is the earliest form of breast cancer.

The breast cancer incidence rate, a measure of the number of new breast cancers per 100,000 women, increased nearly 4% per year during the 1980s. During the 1990s, this rate of increase slowed. The incidence is now increasing at less than 1% per year.

In 2003, about 39,800 women will die from breast cancer in the US. Breast cancer is the second leading cause of cancer death in women, exceeded only by lung cancer.