Tumor suppressor genes are frequently methylated in lymph node metastases of breast cancers

Introduction: Metastasis represents a major adverse step in the progression of breast carcinoma. Lymph node invasion is the most relevant prognostic factor; however little is known on the molecular events associated with lymph node metastasis process. This study is to investigate the status and role of methylation in lymph node metastatic tumors. Materials and methods: Bisulfite pyrosequencing is used to screen 6 putative tumor suppressor genes (HIN-1, RASSF1A, RIL, CDH13, RAR beta 2 and E-cadherin) in 38 pairs of primary breast tumors and lymph node metastases. Results: We found that HIN-1, CDH13, RIL, RASSF1A and RAR beta 2 were frequently methylated both in primary and metastatic tissues (range: 55.3%similar to 89.5%). E-cadherin was not frequently methylated in either setting (range: 18.4%similar to 23.7%). The methylation status of HIN-1, CDH13, RIL, and RAR beta 2 in lymph nodes metastasis were correlated with that in primary tumors. The Pearson correlation values ranged from 0.624 to 0.472 (p values < 0.01 to 0.001). Interestingly, we observed an association between HIN-1 methylation and hormone status in metastatic lymph nodes. Hypermethylation of HIN-1 in metastasis lymph nodes was significantly associated with expression of ER (odds ratio, 1.070; P = 0.024) and with PR (odds ratio, 1.046; P = 0.026). Conclusions: This study suggests that hypermethylation of tumor suppressor genes is extended from primary to metastatic tumors during tumor progression.