DNA Methylation Changes in Sera of Women in Early Pregnancy are Similar to Those in Advanced Breast Cancer Patients (Technical Briefs‪)‬

In normal human pregnancy, the uterus and its arterial system, including the decidua and the adjacent third of the myometrium, are invaded by cytotrophoblasts (1, 2), which initiate conversion of the decidual vascular system from a high-pressure/low-flow system to a low-pressure/high-flow system that meets the needs of the fetus and placenta (3). The trophoblastic invasion in humans occurs between weeks 8 and 18 of pregnancy (4). The invasion process into the uterus shows many similarities to the invasion of malignant cells during metastasis in that both types of cells have to pass through a basal membrane (5). One of the most important diseases of pregnant women, preeclampsia, is known to be associated with a failure of complete trophoblastic invasion in the first third of the myometrium (6). Epigenetic alterations, including changes in DNA methylation status, are among the most common molecular alterations in human neoplasia (7). DNA methylation changes are also involved in mammalian development, starting with a wave of demethylation during cleavage, followed by genome-wide de novo methylation after implantation (8). Recently, Ohgane et al. (9) reported that the differentiation of a trophoblast lineage is associated with DNA methylation and demethylation. In many cases, aberrant methylation of the CpG island genes has been correlated with a loss of gene expression, and it has been proposed that DNA methylation provides an alternative to gene deletion or mutation for the loss of gene function (7). Moreover, it is now widely known that methylated DNA can be detected in various body fluids, including serum and plasma, and that the methylation status of some genes can be used for early detection of, or even risk assessment for, various types of human neoplasia (10).