Mammographic Density and the Risk and Detection of Breast Cancer

TLDR

Extensive mammographic density increases breast cancer risk and hampers mammographic detection, yet its impact varies by detection method. The study assessed how baseline mammographic density predicts breast cancer risk across detection methods, screening intervals, and age groups. Three nested case‑control studies of 1,112 matched pairs in screened populations were conducted to evaluate this association. Women with ≥75 % dense breast tissue had a 4.7‑fold higher breast cancer risk, with odds ratios of 3.5 for screening‑detected cancers and 17.8 for cancers found within 12 months of a negative exam, and this elevated risk persisted for at least eight years, especially in younger women, with density accounting for 26 % of all cancers and 50 % of early post‑negative detections.

Abstract

Extensive mammographic density is associated with an increased risk of breast cancer and makes the detection of cancer by mammography difficult, but the influence of density on risk according to method of cancer detection is unknown.We carried out three nested case-control studies in screened populations with 1112 matched case-control pairs. We examined the association of the measured percentage of density in the baseline mammogram with risk of breast cancer, according to method of cancer detection, time since the initiation of screening, and age.As compared with women with density in less than 10% of the mammogram, women with density in 75% or more had an increased risk of breast cancer (odds ratio, 4.7; 95% confidence interval [CI], 3.0 to 7.4), whether detected by screening (odds ratio, 3.5; 95% CI, 2.0 to 6.2) or less than 12 months after a negative screening examination (odds ratio, 17.8; 95% CI, 4.8 to 65.9). Increased risk of breast cancer, whether detected by screening or other means, persisted for at least 8 years after study entry and was greater in younger than in older women. For women younger than the median age of 56 years, 26% of all breast cancers and 50% of cancers detected less than 12 months after a negative screening test were attributable to density in 50% or more of the mammogram.Extensive mammographic density is strongly associated with the risk of breast cancer detected by screening or between screening tests. A substantial fraction of breast cancers can be attributed to this risk factor.