To explore the relationship between methylation status of XAF1 (X-linked inhibitor of apoptosis protein associated factor-1) gene promoter and its protein expression in papillary thyroid carcinoma (PTC).Methylation-specific polymerase chain reaction (MSP) and immunohistochemical substance P (SP) technique were used to detect the methylation status of XAF1 gene promoter and its protein expression in 70 PTC cases and their matched adjacent non-cancerous epithelium (NCE).In NCE, there was no promoter methylation of XAF1 gene while the rate was 35.7% (25/70) in PTC (χ(2) = 27.206, P0.01). And it was correlated with tumor TNM stage, pathological grade and lymph node metastasis (P0.05). The positive rates of XAF1 protein expression in NCE and PTC were 100% (70/70) and 55.7% (39/70) respectively. And there was significant difference (χ(2) = 36.458, P0.01). In PTC, the positive rates of XAF1 protein expression in Grades I and II were 67.5% (27/40) and 40.0% (12/30) respectively. And they were 35.7% (10/28) and 69.0% (29/42) in the lymph node metastasis and non-metastasis groups respectively. And there were significant differences between two groups (P0.05). Futhermore, there was distinct correlation between methylation of XAF1 gene promoter and its protein expression (χ(2) = 8.864, P0.01).Methylation of promoter may be one of the important inactivating factors of XAF1 gene. And it plays an important role in the carcinogenesis and progression of PTC.
