Fifteen genes of the “Claudin.low” gene signature had CpG sites with varying methylation pattern over these BC cell lines which was significantly higher than expected by chance (hypergeometric testing P_values < 0.001), whereby genes downregulated in “Claudin.low” cancers according to “Claudin.low” signature were methylated and vice-versa, such as “Claudin.low” signature genes such as PRSS8, CLDN4 and VAMP8 were downregulated in “Cluster 2” and their CpG islands were methylated, while genes like SPARC or DDR2 had unmethylated CpG islands and showed higher abundance in these BC cell lines. Here, CLDN4 is linked to cancer.