Somewhat stronger associations were observed between PGRMC1 and TK1 expression within the basal subtype (r = 0.241; P = 1.2 × 10−12) and within ER−/HER2− breast cancers (r = 0.256; P = 9.2 × 10−13); however, the magnitude of these associations was smaller than the correlation between PGRMC1 and proliferation scores within these same subsets of patients. This evidence concerns the gene ESR1 and breast cancer.