Breast cancer nodal metastasis correlates with tumour and lymph node methylation profiles of Caveolin-1 and CXCR4

DNA methylation is the best characterised epigenetic change so far. However, its role in breast cancer metastasis has not as yet been elucidated. The aim of this study was to investigate the differences between the methylation profiles characterising primary tumours and their corresponding positive or negative for metastasis lymph nodes (LN) and correlate these with tumour metastatic potential. Methylation signatures of Caveolin-1, CXCR4, RAR-beta, Cyclin D2 and Twist gene promoters were studied in 30 breast cancer primary lesions and their corresponding metastasis-free and tumour-infiltrated LN with Methylation-Specific PCR. CXCR4 and Caveolin-1 expression was further studied by immunohistochemistry. Tumours were typified by methylation of RAR-beta and hypermethylation of Cyclin-D2 and Twist gene promoters. Tumour patterns were highly conserved in tumour-infiltrated LN. CXCR4 and Caveolin-1 promoter methylation patterns differentiated between node-negative and metastatic tumours. Nodal metastasis was associated with tumour and lymph node profiles of extended methylation of Caveolin-1 and lack of CXCR4 hypermethylation. Immunodetection studies verified CXCR4 and Caveolin-1 hypermethylation as gene silencing mechanism. Absence of Caveolin-1 expression in stromal cells associated with tumour aggressiveness while strong Caveolin-1 expression in tumour cells correlated with decreased 7-year disease-free survival. Methylation-mediated activation of CXCR4 and inactivation of Caveolin-1 was linked with nodal metastasis while intratumoral Caveolin-1 expression heterogeneity correlated with disease progression. This evidence contributes to the better understanding and, thereby, therapeutic management of breast cancer metastasis process.