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.