Fascin‐1 as a novel diagnostic marker of triple‐negative breast cancer

In some cases of breast cancer, diagnosis of triple‐negative breast cancer (TNBC) requires further fluorescence in situ hybridization (FISH) for determining human epidermal growth factor receptor 2 (HER2) status. However, few cases undergo FISH in China, leading to difficulty regarding subsequent treatment decisions. Here, we used immunohistochemical analysis to explore expression of fascin‐1, an actin‐bundling protein, as a diagnostic marker of TNBC. A total of 457 cases of breast cancer were divided into four molecular subtypes, including 82 cases (17.9%) of TNBC, 81 (17.7%) of HER2‐enriched, 185 (40.5%) of luminal A, and 109 (23.9%) of luminal B. Positive fascin‐1 expression was seen in 144 cases (31.5%), including 77 (16.8%) strong positive cases. Rates of positive and strong positive expression of fascin‐1 were significantly higher in cases of TNBC than in the other molecular subtypes. In all cases of breast cancer, the sensitivities and specificities of positive and strong positive fascin‐1 expression for predicting TNBC were 87.8% and 80.8%, and 78.0% and 96.5%, respectively. In cases of hormone receptor–negative breast cancer, the sensitivities and specificities of positive and strong positive fascin‐1 expression for predicting TNBC were 87.8% and 61.7%, and 78.0% and 92.6%, respectively. In 24 cases with estrogen receptor (ER)‐, PR‐, and HER2 2 + equivocal status who underwent FISH, the sensitivity and specificity of strong positive fascin‐1 expression for predicting TNBC were 71.4% and 90.0%. These results suggest that strong positive fascin‐1 expression can be used as a diagnostic marker of TNBC.