Several circadian genes were found in the list of significantly differentially co-expressed genes, some of them presented positive co-expression with PER3 in the LumA breast cancers (DBP, CRY2, PER2, BHLHE41, TEF, and NR1D2) and a loss or a significant reduction of the correlation values was observed in the basal subtype, whereas two circadian genes (ARNTL and RBX1) presented negative or null correlations with PER3 in LumA samples and positive correlations in the basal subtype. This evidence concerns the gene PER3 and breast cancer.