Study: Mammo screening halves breast cancer death risk

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Yet another study has confirmed that screening mammography reduces breast cancer mortality. Women who participated in at least three screening mammograms had a 49 percent lower risk for breast cancer mortality, according to a large case-control study published online Dec. 6 in Cancer Epidemiology, Biomarkers & Prevention.

The study, which included Dutch women who died from breast cancer during 1995 to 2003 matched with a group of controls, showed a robust benefit of early detection by mammography screening in reducing the risk of breast cancer death among women invited to and who attended screening.

Suzie J. Otto, PhD, a senior researcher in the department of public health at the Erasmus Medical Center at Rotterdam in the Netherlands, and colleagues designed the study to focus on the effectiveness of screening in daily practice.

Otto and colleagues mined data from the Netherlands' nationwide screening program and observed 755 patients who died from breast cancer during 1995 to 2003. Each case was matched to five controls on the basis of year of birth, for a total of 3,739 controls.

Among the breast cancer cases, 29.8 percent were detected at screening, 34.3 percent were detected between screenings and 35.9 percent had never been screened.

Women who attended screening tended to have lower grade tumors and their risk for mortality was lower.

According to researchers, 34.2 percent of the screen-detected tumors cases were found at a localized stage, compared with 10.8 percent and 10.3 percent among interval cancers and nonparticipants, respectively.

Stage IV tumors were present in 29.5 percent of the never-screened cases but only 5.3 percent of the screen-detected cases.

Nonparticipants underwent surgery at lower rates than women who attended screening; 53.5 percent of nonparticipants underwent surgery compared with 92.4 percent among women with screen-detected cancers.

If women attended at least three screenings prior to diagnosis, their risk for mortality from breast cancer was reduced by 49 percent. The greatest reduction was seen in women between 70 and 75 years of age, where the reduction in mortality was 84 percent. Among women ages 50 to 69 years, the reduction was smaller, at 39 percent, but still statistically significant, according to the researchers.

Otto and colleagues noted that the findings are consistent with other recent case-control studies of population-based mammography screening programs in Europe and Australia.

The researchers acknowledged that both screening and treatment advances have contributed to reduced breast cancer mortality. Although they were unable to disentangle the contribution of treatment in this study, they wrote, “We observed that women with breast cancer who died of the disease less often underwent surgery compared with those still alive, which is likely according to their advanced stage at diagnosis as emphasized by the high proportion of surgery among the screen-detected cases.” The findings reinforce previous studies showing the prognostic value of the method of detection rather than therapeutic intervention among patients with breast cancer.

“Our study adds further evidence that mammography screening unambiguously reduces breast cancer mortality,” said Otto in a statement.