Mammography Screening Reduces Breast Cancer Deaths

Mammography screening may reduce deaths from breast cancer by about 28 percent, according to a study published in BMJ.

Researchers from Norway undertook a prospective cohort study to evaluate the effectiveness of contemporary mammography screening. The study included all Norwegian women, aged 50 to 79, who were followed between 1986 and 2009. A national screening program had been gradually implemented from 1995 to 2005, and biennial invitations were sent to women aged 50 to 69.

The researchers compared deaths from breast cancer among women who were invited to screening with those who were not invited. A clear distinction was made between cases of breast cancer diagnosed before (without potential for screening effect) and after (with potential for screening effect) the first invitation for screening. The Cancer Intervention and Surveillance Modeling Network (CISNET) Stanford simulation model was used to estimate how many women would need to be invited to biennial mammography screening in the age group of 50 to 69  to prevent one breast cancer death during their lifetime.

The results showed that based on 15,193,034 person years of observation, 1,175 of the women invited to screening died from breast cancer, while 8,996 of the women who were not invited died from breast cancer. “After adjustment for age, birth cohort, county of residence, and national trends in deaths from breast cancer, the mortality rate ratio associated with being invited to mammography screening was 0.72 (95 percent confidence interval 0.64 to 0.79). To prevent one death from breast cancer, 368 (95 percent confidence interval 266 to 508) women would need to be invited to screening,” the authors wrote.

The invitation to mammography screening appeared to be associated with a 28 percent reduced risk of death from breast cancer compared with not being invited to screening, the researchers concluded.