HER2 Expression Discordance between Ductal Carcinoma In situ and Invasive Breast Carcinoma. How to Analyze Oncotype DX

Although histologically invasive breast carcinomas can be of no special subtype (ductal) or of special subtypes (as lobular carcinoma), based on their immunohistochemical and molecular features, they are subclassified in four different groups: luminal A, luminal B (with and without HER2 overexpression), HER2 subtype and triple negative. They vary in their gene expression signature, biological potential and clinical course. Luminal A subtype is considered to have a better prognosis and most are treated with hormone therapy alone after surgery because they express hormone receptors and show a low proliferation index. Oncotype DX (ODX) is a molecular score assay that estimates recurrence risk for early-stage hormone receptor-positive, human epidermal growth factor receptor 2 (HER2) negative breast cancer. It can predict which tumours may benefit from adjuvant chemotherapy. It has been reported that occasionally a breast carcinoma can have immunohistochemical and molecular differences between the in situ and the invasive components. We report one case that may lead us to misinterpret ODX results, where the in situ ductal component amplified HER2 gene while invasive component did not. Therefore, carefulness must be taken when evaluating ODX results, and be sure that we are evaluating the invasive component.