Department of Gastroenterological Surgery, Graduate School of Medical Science, Kumamoto University, 1-1-1 Honjo, Kumamoto City, Kumamoto, Japan.
Br J Cancer. 2013 Jul 23;109(2):408-15. doi: 10.1038/bjc.2013.289. Epub 2013 Jun 13.
LINE-1 methylation level is a surrogate marker of global DNA methylation. LINE-1 methylation in primary colorectal cancers (CRCs) is highly variable and strongly associated with a poor prognosis. However, no study has examined LINE-1 methylation levels of metastatic CRCs in relation to prognosis or assessed the heterogeneity of LINE-1 methylation level within the primary CRCs.
Pyrosequencing was used to quantify LINE-1 methylation level in 42 liver metastases, 26 matched primary tumours, and 6 matched lymph node (LN) metastases. KRAS, BRAF, and PIK3CA mutation status and microsatellite instability (MSI) status were also examined.
The distribution of LINE-1 methylation level in liver metastases was as follows: mean, 67.3; range, 37.1-90.1. Primary tumours showed LINE-1 methylation levels similar to those of matched liver and LN metastases. The difference in LINE-1 methylation level between superficial areas and invasive front areas was within 7.0 in all six cases evaluated. Prognostic impact of LINE-1 hypomethylation in liver metastases on overall survival was not observed. The concordance rate was 94% for KRAS, 100% for BRAF, 88% for PIK3CA, and 97% for MSI.
Alteration of LINE-1 methylation level may occur in early CRC tumorigenesis, and the LINE-1 methylation level is relatively stable during CRC progression.
LINE-1 甲基化水平是全基因组 DNA 甲基化的替代标志物。原发性结直肠癌（CRC）中的 LINE-1 甲基化水平高度可变，与预后不良密切相关。然而，尚无研究探讨转移性 CRC 中 LINE-1 甲基化水平与预后的关系，也未评估原发性 CRC 中 LINE-1 甲基化水平的异质性。
采用焦磷酸测序法检测 42 例肝转移灶、26 例配对原发肿瘤和 6 例配对淋巴结（LN）转移灶中的 LINE-1 甲基化水平。同时检测 KRAS、BRAF 和 PIK3CA 基因突变状态以及微卫星不稳定性（MSI）状态。
肝转移灶中 LINE-1 甲基化水平的分布如下：均值为 67.3%；范围为 37.1%-90.1%。原发肿瘤的 LINE-1 甲基化水平与匹配的肝转移灶和 LN 转移灶相似。在所有 6 例评估的病例中，深部区域和侵袭前缘区域的 LINE-1 甲基化水平差异均在 7.0 以内。肝转移灶中 LINE-1 低甲基化对总生存期的预后影响未观察到。KRAS 的一致性率为 94%，BRAF 为 100%，PIK3CA 为 88%，MSI 为 97%。
LINE-1 甲基化水平的改变可能发生在 CRC 肿瘤发生的早期，并且在 CRC 进展过程中 LINE-1 甲基化水平相对稳定。
