Residual glandular tissue (RGT) in BRCA1/2 germline mutation carriers with unilateral and bilateral prophylactic mastectomies

Background: Prophylactic mastectomy (PME) is increasingly performed in women carrying deleterious BRCA1 and BRCA2 germline mutations. The oncologic risk resulting from residual fibroglandular tissue (RGT) is unknown. Methods: All women who had received a mastectomy and at least one postoperative breast MRI, between 2006 and 2016 were extracted from the register of the Center for Hereditary Breast and Ovarian Cancer Cologne (CHBOC). The index MRI was evaluated in terms of basic clinical data and the morphological criteria of RGT. The RGT volume was measured in diameter and was semi-automatically evaluated using software. Results: We identified 169 women carrying BRCA1/2 mutations who underwent prophylactic and curative mastectomy: a total of 338 breasts. RGT was found in 128 of the 338 breasts (37.9%). 68 of the 128 breasts (53.1%) were related to bilateral PME, 37 (28.9%) to unilateral PME and 23 (18.0%) to curative mastectomy. RGT was predominantly unifocal and located in the retroareolar breast region. RGT was observed more often after bilateral PME (p < 0.0001). In this subgroup, the nipple-sparing mastectomy dominated (108 of 136, 79.4%), in contrast to 23 standard mastectomies (23 of 94, 24.5%) in the subgroup of curative mastectomy (23%). There was a trend towards higher amounts of RGT in surgical units with fewer mastectomies performed. During follow-up, two breast cancers were detected after bilateral and unilateral PME, respectively. Conclusions: Our results suggest that the indication for surgery and in particular the selected surgical procedure affect the surgical outcome with respect to RGT. Oncological safety should not be neglected, especially in the high-risk group of BRCA1/2 mutation carriers.