The Dual Role of ABCG2 Copy Number Variation: A Protective Factor in Cancer Risk, and a Prognostic Marker for Survival in Thai Breast Cancer

OBJECTIVE: This study aimed to investigate CNVs of MDR1 and ABCG2 and their associations with clinicopathological characteristics and survival outcomes in Thai breast cancer patients. METHODS: Genomic DNA from 126 breast cancer patients and 162 healthy controls was analyzed. CNVs were determined using real-time PCR and the ∆Ct method. Associations with clinicopathological parameters were assessed using the Chi-square test. Kaplan-Meier survival analysis and the log-rank test, were used to evaluate overall survival. RESULT: The ABCG2 >1/1 genotype was significantly more common in controls than in patients (OR = 0.32, 95% CI: 0.19-0.525, P < 0.001), suggesting a protective role. MDR1 CNVs showed no significant difference between groups. Among breast cancer patients, the MDR1 >1/1 genotype was associated with larger tumor size (>3 cm) and distant metastasis (P = 0.037, 0.008), while the ABCG2 >1/1 genotype was correlated with progesterone receptor positivity and distant metastasis (P = 0.005, 0.046). Survival analysis revealed that ABCG2 >1/1 was associated with shorter overall survival (P = 0.013), whereas MDR1 CNVs showed no significant association with survival (P = 0.127). CONCLUSION: These findings suggest that copy number variations (CNVs) in ABCG2 may serve as both protective and prognostic markers in breast cancer, while MDR1 CNVs may be associated with tumor aggressiveness. Both genes hold potential as biomarkers for breast cancer pathogenesis, clinicopathological characteristics, and survival outcomes in Thai breast cancer patients.