The effects of variations in genomic modules on breast cancer phenotype

The primary aim of this study is to present how expression heterogeneity is reflected in biological processes. We hypothesize that loss of normal regulatory mechanism is related with changed characteristics of a genomic module, which emerges its own phenotypes as a whole. In breast cancer, receptor status is related to degree of cancer variations. In this regard, comparing expression data according to receptor status is a valuable process to prove the hypothesis. For this reason, we investigated differences of genomic modules according to the receptor status. As a result, 4 and 3 genomic modules, which represent distinct biological processes, were obtained from estrogen receptor (ER)-/ progesterone receptor (PR)-positive double positive (DP) and ER-/PR-negative double negative (DN) breast cancer groups, respectively. Comparing the genomic modules between the groups, we found that there were differences of functional roles, which were mainly caused by DP-exclusive genes. The DP-exclusive genes showed variable expressions in the DN group but not in the DP group, and these expression heterogeneities in the DN group reflected transition of the genomic modules to have more malignant properties than in the DP group. In addition, the DP-exclusive genes themselves have a higher possibility to be involved in oncogenic processes in the DN group. In conclusion, this study suggests that expression heterogeneity of the DP-exclusive genes is not a result of deregulation, but a process that drives emergence of novel traits.