[HER2 gene status and mRNA expression in immunohistochemistry 1+ breast cancer]

Objective: To investigate human epidermal growth factor 2 (HER2) gene status and in situ mRNA expression in breast cancers with immunohistochemistry(IHC) 1+ , and to reveal HER2 positive rate in these patients to provide reference data for obtaining precise HER2 results and modifying relevant clinical strategy to breast cancer. Methods: Sixty-five IHC 1+ formalin-fixed and paraffin-embedded samples of invasive breast carcinoma of no special type (IBC-NST) were collected by surgical operation at Peking Union Medical College Hospital during 2011 to 2013. HER2 status and in situ mRNA expression were tested by fluorescence in situ hybridization (FISH) and RNAscope, respectively, by using tissue microarray. Metastatic lymph node was re-tested by FISH if HER2 status was equivocal or negative and with high expression of mRNA in the primary lesion. Results: Four of 65 samples (6.2%) were FISH positive, which included 2 cases of HER2/CEP17>2 and average HER2 copy number>4 and 2 cases of HER2/CEP17<2 and average HER2 copy number>6. In the 4 samples of HER2 positive, 2 patients showed high in situ mRNA expression (3 scores by RNAscope), 2 patients showed moderate in situ mRNA expression (2 scores by RNAscope). In addition, 3 specimens with HER2/CEP17>2 and average HER2 copy number<4 were found in all patients, which included 2 cases of high in situ mRNA expression (3 and 4 scores by RNAscope) and 1 cases of moderate in situ mRNA expression (2 scores by RNAscope). There was no significant association between HER2 status or mRNA expression and clinicopathological characteristics, including tumor size, histopathological differentiation, lymph node metastasis and lymphovascular invasion (P>0.05). Conclusions: A small number of HER2 IHC 1+ patients exist mRNA expression by using FISH method, which suggested that these patients might benefit from anti-HER2 therapy potentially. Since the importance for patients with breast cancers to develop diagnostic and therapeutic strategies from accurate molecular typing, further studies based on a larger cohort are needed to validate our findings.