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The results of a new study suggest that screening mammography reduces subsequent mortality rates from breast cancer for women older than 40 years of age. The results of a study published in the March issue of the International Journal of Cancer suggest that screening mammography reduces subsequent mortality rates from breast cancer for women older than 40 years of age.

Dr. Andrew Coldman and colleagues from the British Columbia Cancer Agency, Vancouver, examined the impact of screening mammography on breast cancer mortality among women who volunteered to be screened by the Screening Mammography Program of British Columbia.

They identified a cohort of women who had at least one mammographic screen between the ages of 40 and 79 years in the period 1988 to 2003. All breast cancer cases and deaths occurring in British Columbia were identified from the British Columbia Cancer registry and linked to the screening cohort.

Incidence and survival rates for women not in the cohort were used to calculate expected deaths from breast cancer in the cohort. The researchers adjusted the data for age and socioeconomic status of the area of residence at the time of diagnosis. Observed breast cancer deaths were divided by expected breast cancer deaths to calculate the breast cancer mortality ratio.

A total of 598,690 women were included in the cohort. The women had undergone a total of 2,196,441 mammograms, with an average of 3.7 screens per woman. Overall, 14,247 breast cancers were identified in the cohort in the study period. A further 19,913 invasive breast cancers were identified in British Columbia women not in the cohort during the study period.

For all ages combined, the mortality ratio was 0.60 (p < 0.0001). In women between the ages of 40 and 49 years at first screening, the mortality ratio was 0.61, which was similar to that seen in women older than 50 years of age.

"Restriction to cases diagnosed before age 50 caused the mortality ratio to increase from 0.61 to 0.65 but it remained significant (p < 0.0001), indicating that the observed mortality reduction was not due to screening after the age of 50 in this group," Dr. Coldman's team explains.

"Correction for self-selection bias using estimates from the literature increased the mortality ratio for all ages to 0.76."

Int J Cancer 2007;120:1076-1080.