Volumetric breast density from full-field digital mammograms and its association with breast cancer risk factors: a comparison with a threshold method.

INTRODUCTION Breast density, a strong breast cancer risk factor, is usually measured on the projected breast area from film screen mammograms. This is far from ideal, as breast thickness and technical characteristics are not taken into account. We investigated whether volumetric density measurements on full-field digital mammography (FFDM) are more strongly related to breast cancer risk factors than measurements with a computer-assisted threshold method. METHODS Breast density was measured on FFDMs from 370 breast cancer screening participants, using a computer-assisted threshold method and a volumetric method. The distribution of breast cancer risk factors among quintiles of density was compared between both methods. We adjusted for age and body mass index (BMI) with linear regression analysis. RESULTS High percent density was strongly related to younger age, lower BMI, nulliparity, late age at first delivery and pre/perimenopausal status, to the same extent with both methods (all P < 0.05). Similarly strong relationships were seen for the absolute dense area but to a lesser extent for absolute dense volume. A larger dense volume was only significantly associated with late age at menopause, use of menopausal hormone therapy, and, in contrast to the other methods, high BMI. CONCLUSION Both methods related equally well to known breast cancer risk factors. IMPACT Despite its alleged higher precision, the volumetric method was not more strongly related to breast cancer risk factors. This is in agreement with other studies. The definitive relationship with breast cancer risk still needs to be investigated.