Abstract PD1-09: High incidence rate of occult cancer in risk reducing mastectomy specimens despite thorough assessment with breast MRI and ultrasound-findings from the hereditary breast and ovarian cancer registration 2016 in Japan
Authors: Yamauchi H , Okawa M , Yokoyama S , Nakamura S , Arai M 
Published: February 2018

Abstract
Introduction:One of the preemptive strategies for Hereditary Breast and Ovarian Cancer (HBOC) is prophylactic surgery. Data for risk reducing mastectomy (RRM) clearly showed a risk reduction of more than 90% for breast cancer.
Method: We report here the statistical results of the HBOC registration up to 2016. The subjects of this study were those who underwent BRCA1/2 genetic testing during the study period, at 7 medical institutions.
Results: A total of 1527 probands underwent BRCA testing; 1125 cases (73.7%) were negative for BRCA1/2 mutation, and 297 cases (19.5%) were positive, while 105 cases (6.9%) had uncertain results. Among the 297 cases with positive results, 157 cases (10.3%) were positive for BRCA1, 139 cases (9.1%) for BRCA2, and 1 case (0.1%) was positive for both.The mean age at breast cancer diagnosis was 41.7 years in BRCA1/2 mutation positive and 45.8 years in negative cases. In comparison to the National Registration for Breast Cancer Incidence 2011 in Japan (n=72,472), breast cancer with BRCA mutations occurred at a younger age. Among 359 cases of triple negative breast cancer, 101 cases (28.3%) were BRCA1 mutation positive while 18 cases (5.0%) were BRCA2 mutation positive.
Three hundred seventy cases underwent genetic testing prior to surgery, as a deciding factor for the surgical procedure. Among BRCA mutation positive cases, 58 cases (87.9%) chose to undergo total mastectomy, and 8 cases (12.1%) chose breast conserving surgery (BCS); on the other hand, 141 cases (46.4%) of BRCA mutation negative cases chose total mastectomy and 158 cases (52.0%) chose BCS.
Four cases of new onset breast cancers were observed among the 55 cases of previvors (mean observation period: 2.5 years; incidence rate: 2.9%/Y). Among the 73 BRCA1/2 mutation positive women who underwent BCS, 3 ipsilateral breast cancer cases were observed (mean observation period: 3.5 years; incidence rate: 1.2%/Y), while 2 cases were noted among 477 cases of BRCA1/2 mutation negative cases (mean observation period: 2.2 years; incidence rate: 0.2%/Y). Of 189 BRCA1/2 mutation positive cases with unilateral breast cancer, 8 contralateral breast cancer cases were noted (mean observation period: 3.0 years; incidence rate: 1.4%/Y), while 4 cases of contralateral breast cancer were observed among 892 cases of BRCA1/2 mutation negative cases (mean observation period: 2.2 years; incidence rate: 0.2%/Y).
Fifty-one patients had undergone RRM.Six cases (11.8%) of occult breast cancer were noted in the RRM specimens, among which 2 were BRCA1 positive cases and 4 were BRCA2 positive cases. All of these six cases had undergone extensive imaging work-up prior to surgery by using mammography, ultrasound and breast MRI.
Conclusions: The incidence rate of occult cancer after risk-reducing mastectomy was reported to be about 5% in the high-risk population. Our report showed a relatively higher incidence rate of occult cancer at 11.8% among BRCA mutation positive cases, despite thorough pre-operative radiological evaluations, which included a breast MRI. These results suggest the limitations in the use of MRI for the surveillance of patients with BRCA mutations.
Citation Format: Yamauchi H, Okawa M, Yokoyama S, Nakamura S, Arai M. High incidence rate of occult cancer in risk reducing mastectomy specimens despite thorough assessment with breast MRI and ultrasound-findings from the hereditary breast and ovarian cancer registration 2016 in Japan [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr PD1-09.