Background Recently, we reported the identification of a previously uncharacterized and evolutionarily conserved gene, fragile-site associated tumor suppressor (FATS), at a frequently deleted region in irradiation (IR)-induced tumors.However, the role of FATS in breast cancer development and its clinical significance has not been defined. The aim of this study was to determine the role of FA7S in breast cancer development and to evaluate its clinical significance in breast cancer.Methods The expression level of FATS mRNA was determined in 106 breast carcinomas and 23 paired normal breast tissues using quantitative real time reverse transcription-polymerase chain reaction (RT-PCR). The relationship between FATS expression and clinicopathological parameters were also analyzed.Results The mRNA level of FATS was down-regulated in breast cancer compared with paired normal tissues. Low expression of FATS was correlated with high nuclear grade. There was a tendency to a favorable outcome for patients with high expression of FATS (P=0.346). However, low expression of FATS was associated with poor outcome of breast cancer patients with node positive (P=0.011). Furthermore, the mRNA level of FATS showed an independent value in predicting the outcome of breast cancer patients with positive lymph nodes.Conclusion FATS is involved in the carcinogenesis and development of breast cancer and could be a potential biomarker and prognostic factor for breast cancer therapy.