Breast Density and Screening Mammography Outcomes

Prior to 2009, the US Preventive Services Task Force guidelines recommended that women 50 to 74 years of age receive a screening mammogram every 1 to 2 years. In 2009, the task force revised those guidelines, calling for biennial mammography for women in that age group. The updated guidelines did not consider the influence of breast cancer risk factors other than age, and, according to researchers, women with risk factors that increase the likelihood of advanced-stage breast cancer at diagnosis may benefit from more frequent screening.

One such factor is high breast density, which is associated with larger tumor size, positive lymph nodes, and advanced-stage disease. Women who used postmenopausal estrogen plus progestogen for ≥5 years also have an increased risk of development and diagnosis of breast cancer at an advanced stage, and the risk is further increased in women with dense breasts who use postmenopausal hormone therapy (HT).

Researchers recently conducted a prospective cohort study to compare the benefits and harms of screening mammography frequencies according to age, breast density, and postmenopausal HT use. They reported results of the study in JAMA Internal Medicine [2013;173(9):807-816].

The study population included 11,474 women with breast cancer. The majority were ≥50 years of age (83.2%) and white (86.4%); 56.5% had heterogeneously dense or extremely dense breasts. Percentages of interval cancers increased with more frequent screenings.

High breast density was defined as heterogeneously dense or extremely dense; low or average breast density was defined as fatty or scattered fibroglandular densities. The proportion of tumors associated with less favorable prognostic characteristics (stage IIb or higher, size >20 mm, and positive lymph nodes) was higher among women with high breast density compared with women with low or average breast density.

Within density categories, the proportion of women with less favorable prognostic tumor characteristics did not vary by screening interval, with the exception of women with extremely dense breasts. For those women, a 3-year screening interval was associated with a higher proportion of advanced stage, large tumors, and positive lymph nodes.

Compared with annual mammography, for women 50 to 74 years of age, biennial mammography does not increase the risk of tumors with advanced stage or large size regardless of breast density or HT use. For women 40 to 49 years of age with extremely dense breasts, biennial mammography versus annual is associated with increased risk of advanced-stage cancer (odds ratio [OR], 1.89; 95% confidence interval [CI], 1.06-3.39) or large tumors (OR, 2.39; 95% CI, 1.37-4.18).

The cumulative probability of at least 1 false-positive mammography result after 10 years was highest among women 40 to 49 years of age undergoing annual screening with heterogeneously dense (68.9%) or extremely dense breasts (65.5%).

The estimated cumulative probability of a woman receiving at least 1 false-positive biopsy recommendation after 10 years followed a similar pattern to that of false-positive mammography results: (1) the risk decreased as screening interval increased; (2) risk was lowest among women with fatty breasts, and (3) risk was highest among combination HT users with dense breasts.

In summary, the researchers said, “Women 50 to 74 years of age, even those with high breast density or HT use, who undergo biennial screening mammography have similar risk of advanced-stage disease and lower cumulative risk of false-positive results than those who undergo annual mammography.”

They added a note on the relevance of their findings: “When deciding whether to undergo mammography, women 40 to 49 years of age who have extremely dense breasts should be informed that annual mammography may minimize their risk of advanced-stage disease, but the cumulative risk of false-positive results is high.”