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Updated: May 7, 2026
Building Up a High-throughput Screening Platform to Assess the Heterogeneity of HER2 Gene Amplification in Breast Cancers
Published on: December 5, 2017
HER2 testing of multifocal invasive breast carcinoma: how many blocks are enough?
Gillian C Bethune1, J Brendan Mullen, Martin C Chang
1Dept of Pathology and Laboratory Medicine, Mount Sinai Hospital, 600 University Ave, 6-500, Toronto, ON M5G 1X5, Canada;
Objectives:
To determine the diagnostic yield of testing multiple blocks for HER2 in cases of multifocal breast carcinoma.
Methods:
We identified 246 consecutive cases of multifocal invasive breast carcinoma in which HER2 was tested on more than 1 tumor focus. We performed an audit of all cases with respect to tumor size, grade, and histologic type.
Results:
HER2 status was concordant between multiple foci in 230 (93.5%) of 246 cases, with the largest focus having the most positive HER2 result in 242 (98.4%) of 246 cases. We did not find a single case in which a smaller focus demonstrated a more positive HER2 status unless this focus was either higher grade or different histologically.
Conclusions:
Our findings support the evaluation of HER2 on the largest focus, with additional testing on smaller foci having a different histologic type or higher grade.
