Preferential HER-2/neu overexpression and/or amplification in aggressive histological subtypes of invasive breast cancer

Aims: To investigate whether alterations of the HER2 gene occur more frequently in histologically unfavourable subtypes of invasive breast cancer. Methods: The study was composed of nine invasive apocrine, six lipid‐rich, 12 glycogen‐rich, 11 micropapillary and 33 pleomorphic lobular breast carcinomas. Lymph node involvement was represented in all subgroups. HER2 status was confirmed in all cases by using immunohistochemistry (CB11, Herceptest) and fluorescent in‐situ hybridization (FISH) analysis (Vysis). Results: Micropapillary and apocrine carcinomas showed the highest rate of protein overexpression (72% and 66%) and gene amplification (45% and 44%). Protein overexpression was common in poorly differentiated pleomorphic lobular carcinomas (56%); however, this subgroup failed to show an increased number of gene copies by FISH (31%). The incidence of HER2 overexpression (33% and 50%, respectively) and gene amplification (25% and 33%, respectively) among glycogen‐rich and lipid‐rich carcinomas was not higher than that observed in breast cancer generally. Conclusion: Our data suggest that preferential involvement of the HER2 gene in micropapillary and apocrine breast carcinomas may contribute to their aggressive behaviour.