Background: High density breast mammography has been associated with a greater risk for breast cancer and an increased likelihood of false negative results. 

Objectives: To assess whether the degree of mammographic breast density correlates with an increased risk for the presence of radiographic findings requiring further histological investigation. 

Methods: Included in the study were 2760 consecutive screening mammograms performed in a large volume, early detection mammography unit. All mammograms were complemented by high resolution ultrasound and interpreted by a single expert radiologist. Breast density (BD) was evaluated using a semi-quantitative 5 grade scale and grouped into low breast density (LBD) and high breast density (HBD) mammograms. Demographic and all relevant obstetric, personal and family history of breast cancer data were recorded. 

Results: Of the 2760 mammograms 2096 (76%) were LBD and 664 (24%) were HBD. Mean age of the LBD and HBD groups was 59 ± 10.5 and 50.9 ± 9.3 years respectively (P = 0.001). Breast density significantly correlated with presence of mammographic findings requiring further histological assessment (8.7% and 12.3% for LBD and HBD respectively, P < 0.01). In women younger than 60 years in whom histological assessment was required due to these findings, malignant pathology was significantly more prevalent in the HBD group (2.3% and 4.1% respectively, P = 0.03). Age, parity, patient history and HBD were identified as independent risk factors for any pathological mammographic finding. 

Conclusions: Highly dense mammography, aside from being an indicator of higher risk for breast cancer, appears to be associated with a significantly higher incidence of findings that will prompt further investigation to achieve a definite diagnosis.