MRI Volumetric Analysis of Breast Fibroglandular Tissue to Assess Risk of the Spared Nipple in BRCA1 and BRCA2 Mutation Carriers

Abstract

Prophylactic nipple-areolar complex (NAC)-sparing mastectomy (NSM) in BRCA1/2 mutation carriers is controversial over concern regarding residual fibroglandular tissue (FGT) with malignant potential. The objective of this study was to model the volume of FGT in the NAC at a standard retroareolar margin (5 mm) and examine the change in this amount with a greater retroareolar margin or areola-sparing technique. A segmentation protocol was applied to breast MRIs from 105 BRCA1/2 patients to quantify volumes of FGT for total breast and NAC. The proportion of FGT in the NAC relative to the breast was calculated as the primary outcome and was compared for 5 mm versus 10 mm retroareolar depths. The proportion of FGT in the areola was compared with the NAC. At 5 mm retroareolar thickness, residual NAC FGT comprised 1.3 % of the total breast FGT. This amount was not significantly greater than the proportion in the areola (p = 0.3, d = 0.1). Increasing the retroareolar thickness to 10 mm led to a statistically and possibly clinically significant increase in the amount of NAC FGT (p < 0.001, d = 1.1). The proportion of FGT remaining in the spared NAC with a 5 mm margin is extremely small, suggesting that leaving the entire NAC would create very little added risk. Doubling the retroareolar margin may translate into a clinically meaningful increase. Overall, our findings support the safety of the current trend toward increased rates of prophylactic NSM performed in this high-risk population.