As the debate continues over the benefit of screening mammography for women aged 40 to 49, research from Swedish Cancer Institute in Seattle has found that breast cancers detected by mammography in this age group have a better prognosis than those detected by other means, according to a study published in the March edition of Radiology.

While the American Cancer Society and other medical organizations recommend that women begin receiving annual screening mammograms at age 40, the U.S. Preventive Services Task Force issued controversial guidelines in 2009 stating that the benefits of screening for women aged 40 to 49 were potentially outweighed by the harms, such as false-positive results. Judith A. Malmgren, PhD, president of HealthStat Consulting, and colleagues wanted to examine the benefit of mammography for this specific group of women.

“Our goal was to assess the differences between mammography and non-mammography detected breast cancer, to determine whether earlier detection confers a treatment and morbidity advantage because the disease is found at an earlier stage,” Malmgren said in a statement.

The research team reviewed breast cancer patient data from a dedicated registry at Swedish Cancer Institute’s community cancer center. Data on 1,977 breast cancer patients between the ages of 40 and 49 who were treated between 1990 and 2008 were analyzed, with the researchers tracking the method of diagnosis (detected by mammography, patient or physician), stage at diagnosis, treatment and follow-up information such as disease recurrence.

Results showed a dramatic increase in the percentage of mammography-detected breast cancers over the study period. In 1990, 27.5 percent of breast cancer patients had tumors detected by mammography, with the rest having either physician or patient-detected tumors. By 2008, the proportion of mammography-detected breast cancer had increased to 58 percent, with the remaining 42 percent detected by the patient or physician examination.

Over the 18-year period, the number of breast cancers diagnosed at Stage 0 increased by 66 percent, while the number of Stage III breast cancers decreased by 66 percent. The majority of Stage 0 cancer cases were ductal carcinoma in situ.

“Stage is a critical factor in the decision-making process as to whether or not to administer chemotherapy, and patients with [mammography-detected] breast cancer have more favorable prognostic factors, such as estrogen receptor positivity and proportionally lower-stage disease, resulting in the receipt of significantly less surgical and chemotherapy treatment,” wrote the authors.

Compared with women whose cancer was self-detected or discovered by a physician, patients whose cancer was detected using mammography were more likely to have breast-conserving treatment and less likely to have chemotherapy. Specifically, they were more likely to undergo lumpectomy (67 percent versus 48 percent), less likely to undergo modified radical mastectomy (25 percent versus 47 percent), and less likely to die of breast cancer (4 percent versus 11 percent).

“The shift toward more mammography-detected breast cancer cases was accompanied by a shift toward diagnosis at an earlier stage of disease that required less treatment,” said Malmgren. “The objective of screening is to detect disease at an earlier, more treatable stage, which—based on our review—mammography accomplishes.”

For more from Health Imaging on screening mammography, read "USPSTF Guidelines: Two Years Later the Fallout Continues."