Background: XIST gene is a long noncoding RNA that has been implicated 
strongly in the process of X chromosome inactivation during early 
embryogenesis. Its expression is frequently lost in some female's cancer. In 
breast cancer, XIST gene deletion is a point of much interest, and its role as a 
prognostic marker is yet unclear.
Aim of the Work: is to detect XIST gene deletion by fluorescence in situ 
hybridization and to correlate this deletion with the clinicopathological data of 
breast cancer patients.
Subjects and Methods: This research was a prospective study conducted on 
sixty recently diagnosed female breast cancer cases who underwent mastectomy 
at South Egypt Cancer Institute, Assiut University, in the period from December 
2019 to December 2021, and 30 apparently healthy breast tissues from 
mastectomy specimens due to proliferative breast diseases or granulomatous 
mastitis were included as a control group. XIST gene deletion was detected by 
fluorescence in situ hybridization.
Results: XIST gene was significantly deleted in patients with breast cancer 
(P<0.001). This deletion was significantly associated with older age (P = 0.026), 
positive nodal metastasis (P = 0.005), and advanced tumor stage (P=0.028) but 
was not related to tumor size (P = 0.501) or CA 15.3 (P = 0.905). Also, XIST 
gene deletion was more prevalent among patients with triple-negative breast 
cancer (P = 0.009).
Conclusion: XIST gene was deleted among BC patients. XIST gene deletion 
was more prevalent among patients with TNBC.XIST gene deletion could be 
considered as an important predictive biomarker in breast cancer and an 
indicator of poor clinical outcome.