Low values of PER3 expression were found to be significantly associated to worse relapse-free survival outcomes in both, the complete dataset (HR = 0.61, p-val = 8.6 × 10−15) and in LumA samples (HR = 0.51, p-val = 5.3 × 10−11) but not in the rest of breast cancer subtypes. Here, PER3 is linked to breast cancer.