Breast Cancer Res Treat 2016 Feb 18
Low prevalence of HER2 positivity amongst BRCA1 and BRCA2 mutation carriers and in primary BRCA screens.   
The aim of this study is to delineate more clearly the prevalence of HER2+ breast cancer in women with germline BRCA1/2 mutations. For this purpose, we analysed primary mutation screens on women with breast cancer with unequivocal HER2 amplification and assessed the proportion of BRCA1 and BRCA2 breast cancers that were HER2+ comparing this with the existing literature. The results are that 1063 primary BRCA screens had confirmed tumour HER2 status. If HER2+ only 2.5 % (4/156) and 3.2 % (5/156) of women had a BRCA1 or BRCA2 mutation identified respectively; compared to 27.7 % (115/415) and 8.2 % (34/415) with triple negative tumours. Only 2.1 % (4/195) women with BRCA1-related breast cancer had HER2 amplified breast cancers rising to 6.8 % (n = 12, p = 0.04) in BRCA2. These rates are in keeping with most of the existing literature except a recent large multicenter report which documented higher rates but with no control group. The study concluded that true HER2-amplified breast cancers are rare amongst BRCA1 mutation carriers and are less common in BRCA2 than background rates.

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Does your approach differ across the HER2 IHC spectrum?