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. 2013 Oct;140(4):588-92.
doi: 10.1309/AJCPZSV2W1CPGRJW.

HER2 testing of multifocal invasive breast carcinoma: how many blocks are enough?

Gillian C Bethune  1 , J Brendan Mullen, Martin C Chang
Affiliations

HER2 testing of multifocal invasive breast carcinoma: how many blocks are enough?

Gillian C Bethune et al. Am J Clin Pathol. 2013 Oct.

Abstract

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.

Keywords: Breast carcinoma; FISH; HER2; Immunohistochemistry; Multifocal.

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