To assess the function of the CK2–HTATSF1–TOPBP1 axis in breast tumors, we examined the expression of HTATSF1 and TOPBP1, as well as the level of HTATSF1 pS748 in an immortalized but nontransformed human breast epithelial cell MCF10A, human mammary epithelial cells (HMECs), and breast cancer cells of different molecular subtypes, including T-47D, SK-BR-3, BT-549, and MDA-MB-231 cells. Here, TOPBP1 is linked to breast cancer.