Absence of Glutathione S-Transferase Theta 1 Gene is Significantly Associated with Breast Cancer Susceptibility in Pakistani Population and Poor Overall Survival in Breast Cancer Patients: A Case-Control and Case Series Analysis

PurposeDeletion of Glutathione S-Transferase Theta 1 (GSTT1) encoding gene is implicated in breast cancer susceptibility, clinical outcomes, and survival. Contradictory results have been reported in different studies. The present investigation evaluated GSTT1-absent genotype for its contribution to breast cancer risk in Pakistani population and specific clinical outcomes in breast tumours. MethodsA prospective study comprising case-control analysis and case series analysis components was designed. Peripheral blood samples were collected from enrolled participants. After DNA extraction, GSTT1 genotyping was carried out by a multiplex PCR with {beta}-globin as an amplification control. Association evaluation of GSTT1 genotypes with breast cancer risk, specific tumour characteristics, and survival was the primary endpoint. ResultsA total of 264 participants were enrolled in the molecular investigation (3 institutions). The study included 121 primary breast cancer patients as cases and 143 age-matched female subject, with no history of any cancer, as controls. A significant genetic association between GSTT1-absent genotype and breast cancer susceptibility (p-value: 0.003; OR: 2.13; 95% CI: 1.08-4.29) is reported. The case-series analysis showed lack of association of GSTT1 genotypes with tumour stage (p-value: 0.12), grade (p-value: 0.32), and size (p-value: 0.07). The survival analysis revealed that GSTT1-absent genotype cases had a statistically significant shorter overall survival (OS) than those with GSTT1-present genotype cases (mean OS: 23 months vs 33 months). The HR (95% CI) for OS in patients carrying GSTT1-absent genotype was 8.13 (2.91-22.96) when compared with GSTT1-present genotype. ConclusionsThe present study is the first report of an independent, population-oriented significant genetic association between GSTT1-absent genotype and breast cancer susceptibility as well as OS in breast cancer cases. Upon further validation, GSTT1 variation may serve as a marker for devising better and population-specific strategies for screening and treatment in breast cancer management.