FAT1 expression in different breast lesions and its down-regulation in breast cancer development

Background: Breast cancer is one of the most common cancers in women and the mechanisms under the progression from ductal carcinoma in situ (DCIS) to invasive ductal carcinoma (IDC) remain incompletely understood. FAT1 is an important tumor regulatory factor. The aim of the study is to detect the possible discrepancy in their expression about FAT1 in different breast lesions and to explore the role of FAT1 in the development of breast cancer. Patients and methods: We used immunohistochemistry to detect protein expression of FAT1 in 10 patients diagnosed with breast benign disease, 5 patients diagnosed with DCIS, 5 patients diagnosed with IDC and 25 patients diagnosed with invasive ductal carcinoma and accompanying ductal carcinoma in situ (IDC-DCIS). Results: FAT1 cadherin was expressed by both neoplastic and non-neoplastic mammary epithelia. FAT1 cadherin expression was not significantly changed in DCIS group in comparison with the benign group (P=0.392). Comparing with the DCIS group, expression in the IDC group appeared to be down-regulated. There was a significant difference for the positive rate between the DCIS and IDC group (P=0.048). In the IDC-DCIS group, the total staining score of the IDC component was significantly lower than the score of DCIS component (P=0.002). Conclusions: FAT1 cadherin expression was found to be significantly decreased in IDC group compared with the DCIS group, which indicated it might have tumor suppressive function in late stage of breast cancer development. FAT1 cadherin can be identified as a new biomarker in clinical practice.