Epigenetic variations in breast cancer progression to lymph node metastasis

Breast cancer is a heterogeneous disease characterized by the accumulation of genetic and epigenetic alterations that contribute to the development of regional and distant metastases. Lymph node metastasis (LNM) status is the single most important prognostic factor. Metastatic cancer cells share common molecular alterations with those of the primary tumor, but in addition, they develop distinct changes that allow the cancer to progress. There is an urgent need for molecular studies which focus on identifying genomic and epigenomic markers that can predict the progression to metastasis. The objective of this study was to identify epigenetic similarities and differences between paired primary breast tumor (PBT) and LNM. We employed Methylation-Specific-MLPA (Multiplex ligation-dependent probe amplification) to assess the methylation status of 33 cancer-related genes in a cohort of 50 paired PBT and LNM specimens. We found that the methylation index, which represents the degree of aberrantly methylated genes in a specimen, was maintained during the progression to LNM. However, some genes presented differential methylation profiles. Interestingly, PAX6 presented a significant negative correlation between paired PBT and LNM (p = 0.03), which indicated a switch from methylated to unmethylated status in the progression from PBT to LNM. We further identified that the methylation status of PAX6 on the identified CpG site functionally affected the expression of PAX6 at the mRNA level. Our study unraveled significant epigenetic changes during the progression from PBT to LNM, which may contribute to improved prognosis, prediction and therapeutic management of metastatic breast cancer patients.