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Open Access Highly Accessed Research article

Luminal A and luminal B (HER2 negative) subtypes of breast cancer consist of a mixture of tumors with different genotype

Masumi Yanagawa1, Kenzo Ikemot1, Shigeto Kawauchi1, Tomoko Furuya1, Shigeru Yamamoto2, Masaaki Oka2, Atunori Oga1, Yukiko Nagashima3 and Kohsuke Sasaki1*

Author Affiliations

1 Departments of Pathology, Yamaguchi University Graduate School of Medicine, Ube-shi, 755-8505, Japan

2 Departments of Surgery, Yamaguchi University Graduate School of Medicine, Ube-shi, 755-8505, Japan

3 Division of Breast Disease Surgery, Shimonoseki Kohsei Hospital, Shimonoseki-shi, 750-0061, Japan

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BMC Research Notes 2012, 5:376  doi:10.1186/1756-0500-5-376

Published: 25 July 2012

Abstract

Background

The St Gallen International Expert Consensus 2011 has proposed a new classification system for breast cancer. The purpose of this study was to elucidate the relationship between the breast cancer subtypes determined by the new classification system and genomic characteristics.

Methods

Invasive breast cancers (n = 363) were immunohistochemically classified as follows: 111 (30.6%) as luminal A, 95 (26.2%) as luminal B (HER2 negative), 69 (19.0%) as luminal B (HER2 positive), 41 (11.3%) as HER2, and 47 (12.9%) as basal-like subtypes.

Results

The high expression of Ki-67 antigen was detected in 236 tumors; no cases of luminal A subtype showed high expression of the Ki-67 antigen, but more than 85% of tumors of the other subtypes showed high expression. In addition, DNA ploidy and chromosomal instability (CIN) were assessed using imaging cytometry and FISH, respectively. In this series, 336 (92.6%) tumors consisted of 129 diploid/CIN- and 207 aneuploid/CIN + tumors. Diploid/CIN- and aneuploid/CIN+ features were detected in 64.9% and 27.9% of luminal A, 41.1% and 49.5% of luminal B (HER2-), 11.6% and 81.2% of luminal B (HER2+), 4.9% and 90.2% of HER2, and 17.0% and 76.6% of basal-like subtypes, respectively. Unlike the luminal B (HER2+), HER2 and basal-like subtypes, the luminal A and luminal B (HER2-) subtypes were heterogeneous in terms of DNA ploidy and CIN.

Conclusions

It is reasonable to propose that the luminal A and luminal B (HER2-) subtypes should be further divided into two subgroups, diploid/CIN- and aneuploid/CIN+, based on their underlying genomic status.