Mammography screening reduces breast cancer mortality by about 30% to 40% among participating women.

Omissions

• The 30–40% range applies specifically to women who ATTEND screening; the widely cited figure for women merely INVITED to screening is lower (IARC 2015: about 23% for women aged 50–69), because non-attenders obtain no benefit.
• The effect size is scientifically contested: the Cochrane review (Gøtzsche & Jørgensen) estimates only about a 15% relative reduction in breast cancer mortality, far below the 30–40% figure.
• The claimed range aggregates heterogeneous trials and observational studies of differing design, screening intervals and age groups; some reviews note that observational comparisons between attenders and never-attenders (e.g. Autier 2025, ~45%) are confounded by self-selection (healthy-adherer effect).
• No source specifies the exact reference period or the geographic scope used by the speaker, so the range is a general estimate rather than a figure tied to a specific date or country.

Sources

• AcademicDuffy et al., 'Mammography screening reduces rates of advanced and fatal breast cancers' (PMC, peer-reviewed)Women who participated in mammography screening had a statistically significant 41% reduction in their risk of dying of breast cancer within 10 years
• AcademicZielonke et al., 'Evidence for reducing cancer-specific mortality due to screening for breast cancer in Europe' (ScienceDirect, peer-reviewed)Their average estimate was 40% reduction in the risk of death from BC for women attending mammographic screening
• AcademicLauby-Secretan et al., 'Breast-Cancer Screening — Viewpoint of the IARC Working Group' (NEJM)Women 50 to 69 years of age who were invited to attend mammographic screening had, on average, a 23% reduction in the risk of death from breast cancer
• AcademicAutier et al., 'Evaluation of screening mammography effectiveness' (ScienceDirect, peer-reviewed)compared to women who never attend screening, attenders have a 45 % reduction in their risk
• SecondaryCancer World, Grand Rounds: 'Breast screening' (PDF)invited to screening, was of the order of a 30–40% reduction in breast cancer mortality. This translates to one life saved per 400–500 women screened over 10 [years]
• TertiaryNational Breast Cancer Coalition, 'Mammography for Breast Cancer Screening: Harm/Benefit Analysis' (citing the Cochrane review)According to the Cochrane analysis, mammography decreases the risk of death from breast cancer by about 15% in relative terms, or 0.05% in absolute terms.